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DIN ecological effects Ecological responses of macroinvertebrates and…

- - - - Attributed to lower soil leaching combined with greater
        uptake by plants (pastures, wetland and stream plants),
        in summer-autumn. Quinn & Stroud (2002) found similar
        strong seasonal patterns of DIN in hill country streams
        near Whatawhata in western Waikato
    - - Water quality of a lowland stream in a New Zealand dairy farming catchment
        
        A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m‐3 in winter, with the bulk comprising nitrate nitrogen (NO‐ 3‐N). During summer NO‐ 3‐N was near zero and TN mostly comprised organic nitrogen
- - - - It is concluded that levels of total nitrogen lower than 0.5–1.0 mg TN/L could prevent aquatic ecosystems (excluding those ecosystems with
        naturally high N levels) from developing acidification and eutrophication, at least by inorganic nitrogen pollution. Those relatively low TN levels
        could also protect aquatic animals against the toxicity of inorganic nitrogenous compounds since, in the absence of eutrophication, surface waters It is concluded that levels of total nitrogen lower than 0.5–1.0 mg TN/L could prevent aquatic ecosystems (excluding those ecosystems with
        naturally high N levels) from developing acidification and eutrophication, at least by inorganic nitrogen pollution. Those relatively low TN levels
        could also protect aquatic animals against the toxicity of inorganic nitrogenous compounds since, in the absence of eutrophication, surface waters
      - Ammonium, nitrite, nitrate = most common form of DIN
        
        Come from:
        
        naturally
        
        Atmospheric deopsition
        
        surface and groundwater run-off
        
        dissolution of N-rich geological deposits
        
        N2 fixation by cyanobacteria with heterocycsts
        
        Biological degradation of organic matter
        
        Ammonium to nitrate
        (nitrification)
        
        2 step process, ammonium to nitrite to nitrate
        
        aerobic chemoautotrophic bacteria
        
        Denitrification
        
        Anaerobic conditions needed + bacteria
        
        formation of N2O and N2
        
        Major anthropogenic sources of inorganic nitrogen in aquatic ecosystems
        
        Wastewaters from livestock (cattle, pigs, chickens) farming
        
        Widespread cultivation of N2-fixing crop species, and the subsequent N
        mobilization among terrestrial, aquatic and atmospheric realms
        
        Use of animal manure and inorganic N fertilizers, and the subsequent runoff
        from agriculture
  - - - Despite some improving trends, the current state of water quality in New Zealand lowland rivers is generally poor, as indicated by elevated median nitrogen, phosphorus and E. coli concentrations. The negative relationships between water quality and high-intensity agricultural and urban land cover, and the predominance of pastoral and urban land cover in low-elevation catchments suggests that lowland river water-quality state is strongly influenced by agricultural and urban land use
- - - - The goal of this review is to identify possible causal mechanisms leading to macroinvertebrate and periphyton communities impacts following increases in diffuse DIN, based on literature describing direct and indirect effects. The review also aims to identify important knowledge gaps on the effects of diffuse DIN impacts on macroinvertebrates and periphyton
        
        To ensure a compact overview, this work constrains its focus on causal mechanisms for effects of DIN on macroinvertebrates and periphyton in several ways.
        1) We cite relevant literature as examples of relationships between DIN and macroinvertebrates and periphyton, but do not go into detail on every effect or give details for the different ecosystems in which the studies were undertaken. Where applicable we refer to other review papers.
        2) We treat the effects of DIN on macroinvertebrate and periphyton abundance and diversity as generally negative, since anthropogenic changes following increased DIN is generally regarded as undesirable from a restoration perspective.
        3) Feedback mechanisms and interference from other environmental changes, such as increasing temperatures
        and CO2 levels are not included unless specifically relevant to the example given.
- - - - attempts to link the MCI to instream nitrogen availability in Canterbury have comprehensively demonstrated the lack of a simple or direct relationship (Moore, 2014).
    - - TR no relationship with nutrients
    - - Abundance and composition of periphyton and benthic macroinvertebrates were treated as potential nutrient response variables for 74 streams in montane Colorado. The streams ranged from unenriched to mildly enriched with nutrients (N, P).
        
        Nutrient concentrations were also unrelated to periphyton and macroinvertebrate richness, diversity and community composition. Macroinvertebrate communities did, however, show a strong positive relationship to periphyton abundance
      - Lewis and McCutchan (2010) also reported no
        significant relationship between nutrients and macroinvertebrate
        abundance in river data collected in Colorado, but this study did not include sites that were substantially polluted with nutrients, and the results were acknowledged to be only applicable to nutrient concentrations arising from natural variability and mild anthropogenic enrichment.
    - - A contrasting view of the utility of macroinvertebrates for these
        purposes is provided by Friberg et al. (2010) based on analysis of
        presence–absence macroinvertebrate data from Danish rivers. Although negative responses to total phosphorus and ammoniacal nitrogen were found, no relationship was found with total nitrogen, leading to the conclusion that macroinvertebrates are poor indicators of eutrophication. However this may have been more a consequence of being unable to detect changes in abundance, and the relatively small range of taxa which included few grazers, unlike the study of Smith et al. (2007).
  - - - assessed the effect of whole-stream nitrate enrichment on decomposition of three substrates differing in nutrient quality (alder and oak leaves and balsa veneers) and associated fungi and invertebrates
        
        Nitrate enrichment stimulated decomposition of oak leaves and balsa veneers, fungal biomass accrual on alder leaves and balsa veneers and sporulation of aquatic hyphomycetes on all substrates
        
        abundances or richness of litter-associated invertebrates were not affected by nitrate addition
        
        It appears that microbial nitrogen demands can be met at relatively low levels of dissolved nitrate, suggesting that even minor increases in nitrogen in streams due to, e.g., anthropogenic eutrophication may lead to significant shifts in microbial dynamics and ecosystem functioning.
    - - MCI scores are related to land use through a complex chain of causality, which makes isolating the role of specific variables difficult” (Clapcott and Goodwin, 2014)
    - - General Animal communities are also affected by nitrogen-driven ecosystem changes and several studies describe changes in fauna groups in aquatic and terrestrial systems as a result of increased N deposition (e.g. Berg and Verhoef, 1998; Xu et al., 2009). These papers provide descriptive and correlative changes in patterns for fauna diversity, but lack causal explanations for these changes. Recently, several studies have been published which tested conceptual models on effects of N deposition in food webs, focusing on changes in plant-herbivore relations after releasing primary producers fromN-limitation and altering foliage N content, including consequences for predatory species (Meunier et al., 2016; Pöyry et al., 2016). Comparable to the review on chemical stress (Camargo and Alonso, 2006), they identify possible causal mechanisms by which fauna is affected. However, these studies also show a lack of experimental data and cover only a limited part of this ecologically complex subject.
        
        Also: David R. Lenat,
        J. Kent Crawford
        (1994)
        
        nutrient concentrations were highest at the agricultural site, and the amount of ‘available’ dissolved nitrogen was elevated at both the urban and agricultural sites. Invertebrate taxa richness, a biotic index, and the number of unique invertebrate species (found at only one site) indicated moderate stress (Fair water quality) at the agricultural site
    - - Increase primary producer growth, biomass, proliferation, production (phytoplankton, periphyton, macrophytes)
        
        Decreases resource abundance
        
        change in food plant quality
        
        Many invertebrate species feed on specific periphyton species. Changes in algal and plant species composition due to changes in DIN concentrations can therefore lead to changes in invertebrate community composition. Needs references
        
        Predators and parasitoids depend for their food on the presence of sufficient prey items or hosts
        
        Cashman, M. J., et al. (2013).
        
        The biochemical composition of primary food resources may affect secondary production, growth, reproduction and other physiological responses in consumers and may be an important driver of food-web dynamics. Changes in land use, riparian clearing and non-point nutrient inputs to streams have the potential to alter the biochemical composition of periphyton, and characterising this relationship may be critical to understand the processes by which environmental change can affect food webs and ecosystem function.
        
        1 more item...
        
        In Camargo and Alonso 2006
        
        Leaflitter
        decomposition decreased in atmospherically acidified
        woodland streams because of the negative effects on microbial
        decomposers (bacteria and fungi), with aquatic invertebrates
        (detritivore species, mainly) being affected due to changes in food
        quality and in food availability (Hildrew et al., 1984; Chamier,
        1987; Groom and Hildrew, 1989; Griffith and Perry, 1994;
        Dangles et al., 2004).
        
        Like a decrease in habitat and flow conditions the decrease of resource abundance due to DIN increases is very likely, but again causal evidence on the relationship between N deposition and the decrease of plant-dependent animal species hardly occurs
        
        Creates more homogeneous
        vegetation structure and species diversity,
        
        Decrease availability of reproductive habitat, e.g., egg laying habitat Needs references
        
        Storey et al. 2017 To allow recolonisation and/or persistence of these taxa, restored stream reaches need at least some rocks (or other features) with these characteristics.
        
        impact and alter habitat and flow conditions:
        it can stimulate or enhance the development, maintenance and proliferation of primary producers, resulting in eutrophication of aquatic ecosystems (Camargo and Alonso 2006)
        
        Elevated concentrations of DRP and dissolved
        inorganic nitrogen (NO3-N and NH4-N) may induce
        excessive growths of macrophytes that retard water
        flows and require periodic clearance, such as by
        draglining (Smith et al. 1993).
        
        Duggan et al 2002
        
        The overall structure of invertebrate assemblages appeared to be influenced by a combination of regional differences in substrate type, nutrient concentrations, water clarity, and macrophyte cover
        
        Creates a toxic environment
        
        However, when inorganic nitrogen stimulates growth of toxic algae, cyanobacteria, dinoflagellates and diatoms, fauna can be exposed to high levels of extracellular organic toxins in ambient water and ingestion of intracellular organic toxins.
        
        However, when inorganic nitrogen stimulates growth of toxic algae, cyanobacteria, dinoflagellates and diatoms, fauna can be exposed to high levels of extracellular organic toxins in ambient water and ingestion of intracellular organic toxins. (Camargo and Alonso 2006)
        
        Creates a toxic environment
        
        Increased plant biomass and the subsequent decomposition of organic matter usually lead to low dissolved oxygen levels in water and sediments, especially when water turnover rates are low. Invertebrates as well as fish can die from hypoxia or anoxia or experience toxic stress when reduced oxygen concentrations
        lead to formation of reduced compounds like hydrogen sulphide (H2S) (Camargo and Alonso, 2006).
      - Changes to food web
        
        indirectly through cas-
        cading effects via changes to the quality of food or
        habitat or interspecies interactions, Davis et al. 2010).
    - - Dissolved inorganic nitrogen
        (DIN) was higher in pasture than native streams in
        November-December (Fig. 5C), suggesting a
        strong land use effect with high DIN inputs to
        pasture streams.
        
        More tolerant species found in pasture than native streams
        
        Other studies have also reported greater densities and biomasses in streams with high nutrients compared to pristine streams (Quinn and others 1997),
    - - EPT density and richness, MCI, % non insect taxa had non linear relationships with nutrients. Plus subsidy-stress pattern with increasing pastoral development
      - DIN = measure of agricultural intensity
    - - Urban environment
        
        Aggregate macroinvertebrate biomass was predicted by watershed % impervious surface cover (ISC) (–), conductivity and nutrient concentrations
    - - However, common macroinvertebrate metrics responded more strongly toTN than to DIN, a finding similar
        to those of another study (Fetscher et al. 2014
        
        TN is probably
        the better indicator of ecosystem trophic state than
        DIN (Dodds 2003), so our results suggest that indirect effects
        on macroinvertebrate communities via the eutrophication
        pathway are more likely than direct toxicity effects
        of dissolved N compounds. Macroinvertebrates have
        a strong standing in stream health assessment (Bonada et al.
        2006, Birk et al. 2012), and TN can be related to catchment
        N loading, so we suggest TN is more suitable for objective
        setting than DIN.
        
        We found strong negative relationships between TN
        and %EPT taxa or the MCI, which is a metric calculated
        from tolerance values. These results suggest that N is a
        pervasive stressor for macroinvertebrate communities. Impact
        initiation thresholds of these 2 metrics were ~0.2 mg
        TN/L. A higher impact initiation threshold for EPT richness,
        at ~0.4 mg TN/L, probably reflects that some EPT
        taxa are tolerant to or even benefit from initial nutrient
        enrichment (Wagenhoff et al. 2012).
        
        Therefore, a small increase in the N concentration
        above background levels seems to be associated with
        structural change to different ecosystemcomponents, an observation
        also made by other investigators (Smith and Tran
        2010).
        
        The impact cessation threshold of
        0.5 mg TN/L is well below the 1 mg NO3-N/L objective
        set in New Zealand’s National Objectives Framework
        (MfE 2014) to protect the most sensitive aquatic species
        (including macroinvertebrates) from NO3 toxicity.
    - - The premise that some taxa are intolerant to increasing nutrient
        concentration while others are tolerant underlies a recently developed nutrient index (Smith et al., 2007). A dataset of samples containing macroinvertebrate and chemical data was split roughly equally across a number of bins that covered the nutrient ranges, and weighted averaging
        used to calculate a ‘nutrient optimum’ for each taxon (approximately the mean nutrient concentration of the bin with the largest number of occurrences). The range of optima was then split into eleven groups to assign tolerance values on a scale of 0 (intolerant) to 10 (tolerant). A value of the index, for both nutrients, was then calculated for each sample and shown to correlate reasonably with mean nutrient values, with the conclusion that it provided a robustmeasure of stream nutrient status. A similar approach was taken for data in southeast ueensland, Australia (Haase and Nolte, 2008) but the impact gradient was a linear combination of environmental variables rather than nutrient alone.
    - - The work described has demonstrated some strong associations
        between the abundance levels of some BMWP taxa and nutrient
        levels, especially in the more upland Site Types
        
        At low concentrations the presence of nutrient
        may act to increase food sources, especially algae, causing some
        taxa to thrive and thus act as positive indicators
        
        These latter Site Types are more
        challenging to analyse because of the more complex nature of the pollutant cocktail, and the approach suggested is likely to be less useful (ie more useful at less polluted sites, not so much at more polluted sites
    - - TN had the strongest association with macroinvertebrate species composition. While not reported here, NO3–N concentrations recorded from the MP sites in this study (medians < 3 g m−3; Wilcock et al. 2013a) were all below levels found to be toxic for most freshwater macroinvertebrates (Camargo et al. 2005; Hickey & Martin 2009). This implies that nonlethal factors associated with TN concentration were affecting species composition at those sites.
      - stream macroinvertebrate metrics were found to increase
        along with NOX concentrations following application of integrated catchment management to Waikato hill catchments. postulated
        that the increase in NOX was driven in part by reduced instream uptake of N due to
        increased shading that reduced stream temperatures and instream plants biomass (Quinn et al. 2009).
        
        Hughes and Quinn (2014)
        Whatawhata
  - - - Hill, W. R. and Griffiths, N. A. (2017
        
        3.Snails were less important as nitrogen sinks than as sources of recycled nitrogen in Walker Branch. Over the course of the year, snails excreted approximately 12 times more nitrogen than they accumulated in biomass
        
        Primary consumers like Elimia are important catalysts of nutrient movement through headwater streams, decreasing residence times and facilitating fluxes to downstream waters.
        
        Snails assimilated and excreted up to 50% of the nitrogen initially taken up by autotrophs and leaf microbes, and they were likely to have additional effects on nitrogen spiraling through egestion and the cropping of assimilative biomass.
    - - Therefore, mechanisms behind effects of N deposition on animal species and diversity remain unclear, which hampers optimisation of nature restoration and conservation measures
      - The aim of this review is to identify and structure possible different pathways in which fauna is affected by high N deposition. We identify ten pathways leading to six basic potentially negative bottlenecks: (1) chemical stress, (2) a levelled and humid microclimate, (3) decrease in reproductive habitat, (4) changes in food plant quantity, (5) changes in nutritional quality of food plants and (6) changes in availability of prey or host species due to cumulative effects in the food web. Depending on species and habitat type, different pathways play a dominant role and interference between different pathways can strengthen or weaken the net effect of N deposition.
      - Although all identified pathways and bottlenecks are supported by peer reviewed literature, we conclude that scientific evidence on the causal relationship between increased N deposition and effects on fauna in the complete causal chain is still insufficient. We recommend that future research should aim to clarify the causal mechanisms underlying the observed changes in species composition attributed to N deposition. The most severe gaps in knowledge concern subtle changes in plant chemistry and changes in availability of prey and host species to higher trophic levels.
  - - - Direct and indirect effects of human population density and land use on physical features and invertebrates of Iowa (U.S.A.) streams. "In rural watersheds, high streamwater nitrogen concentrations associated with cultivated land were related to declines in invertebrate taxon richness" but doesn't tease apart as directly causal
    - - Camargo and Ward 1995
        
        Safe concentrations (SCs) of nitrate (NO3N) for early and last instar larvae of two species of Nearctic net-spinning caddisflies. SCs (or 8760 hour LC0.01 values expressed in ppm NO3N) and their 95% confidence limits were 1.4 (0.4 – 3.0) for the early instar of H. occiderualis, 2.4 (0.7 – 5.4) for the early instar of C. pettiti, 2.2 (0.8 – 4.7) for the last instar of H. occidentalis, and 3.5 (1.0–8.1) for the last instar of C. pettiti. These results suggest that larvae of C. pettiti and H. occidentalis may be much more sensitive to nitrate pollution than fishes during long exposures
      - Camargo and Alonso 2006
        
        Can cause chemical stress directly to invertebrates or impact and alter habitat and flow conditions:
        it can stimulate or enhance the development, maintenance and proliferation of primary producers, resulting in eutrophication of aquatic ecosystems; (3) it can reach toxic levels that impair the ability of aquatic animals to survive, grow and reproduce
    - - Chemical stress
        
        Effects of increased nitrogen emissions on aquatic fauna
        were reviewed extensively by Camargo and Alonso (2006) for a wide variety of taxa, including molluscs, planarians, amphipods, decapods, insects and fish. Deposition-derived non-organic N-compounds (NH4 +
        NH3, NO2 −, HNO2, NO3 −) can have direct toxic effects on aquatic fauna (Fig. 1; pathway a) and have been examined by laboratory studies.
        
        The physiological effects can be lethal in case of high toxic concentrations of N compounds, but mostly result in sub-lethal effects associated with reduced feeding activity, fecundity and eventually survival, which decreases population sizes of
        aquatic animals (Camargo and Alonso, 2006).
        
        Intake of nitrate
        (NO3 −) in aquatic animals is much lower than NO2
        − uptake due to low branchial permeability, which makes this compound less toxic. However, nitrate can be converted to nitrite under internal body conditions and subsequently inhibit oxygen transport. Early developmental stages of some marine invertebrates, caddisflies, amphipods and fish seem to be the most sensitive groups. Sensitivity of amphibians to nitrate may also be high and seems connected with decreased body size, fecundity and survival and impaired swimming ability (Camargo and Alonso, 2006).
        
        Discharges from dairy farm waste treatment
        ponds typically have high concentrations of
        ammoniacal nitrogen that are harmful to stream
        animals if not adequately diluted;
        Hickey & Vickers 1994;
        Richardson 1997).
    - - The most prominent macroinivertebrate and periphyton assemblage threshold across the nitrogen (N) gradient was located at very low levels and mainly attributed to declines of multiple taxa. This provided strong evidence for stream assemblages being signiﬁcantly affected when N concentrations exceed reference conditions and for effects cascading through the ecosystem
        
        But no control of other variables. Why N over another?
        
        However, because DIN and TN, DRP
        and TP, as well as TSS and turbidity were highly corre-
        lated with each other (Table 2), only the higher- ranking
        nitrogen, phosphorus, or suspended ﬁne sediment
        attribute was included in the ﬁnal analysis, respectively
        
        Macroinvertebrate and periphyton assemblage turnover was most prominent relative to elsewhere across the entire gra-
        dient at the low end of the N gradient spanning from the
        lowest observed concentrations (0.06 mg TN/L, 0.01 mg
        DIN/L) up to about 0.5 mg TN/L for macroinvertebrates
        and 0.3 mg DIN/L for periphyton
        
        But, they go on to say: Hence, compared to periphyton composi-
        tional turnover, the mechanisms underlying the turnover
        of macroinvertebrate assemblages are more complex
        since the species- speciﬁc responses to increasing N supply
        could be a result of sensitivities to one or multiple envi-
        ronmental effects of eutrophication in addition to inter-
        species interactions as well as due to direct toxic effects
        
        Levels below nitrate toxicity guidelines suggested for freshwater aquatic species in New Zealand Hickey and Martin 2009 = 1.7 mg NO3-N/L for Environments which are
        subjected to a range of
        disturbances from human
        activity.
        
        Threshold implies causative
- - - - However, Phormidium mats do not follow this pattern and tend to proliferate at low to moderate nutrient concentrations (DIN > 0.1–0.2 mg/L and DRP < 0.01 mg/L; Heath et al. 2015, McAllister et al. 2016).
        
        Internal processes also may play a role in maintaining growth once mats are established (Wood et al. 2015
  - - - variability in algal biomass in this study was not related to in-stream concentrations of TIN
        However, neither TIN nor SRP were low enough at our study sites to be considered limiting
        Postulated that temperature was more important driver of periphyton biomass
    - - Abundance and composition of periphyton and benthic macroinvertebrates were treated as potential nutrient response variables for 74 streams in montane Colorado. The streams ranged from unenriched to mildly enriched with nutrients (N, P).
        
        The study showed no meaningful relationship between periphyton biomass accumulation and concentrations of total or dissolved forms of nitrogen or phosphorus. Nutrient concentrations were also unrelated to periphyton richness, diversity and community composition.
        
        Our study suggests that the nutrient response is suppressed by other controlling factors on the lower limb of the nutrient response curve (i.e. at low nutrient concentrations); a quantitatively significant response occurs only in excess of a threshold beyond which nutrients become dominant over other controlling factors. This interpretation of the results is consistent with published meta-analyses showing lack of nutrient response for a high proportion of experimentally enriched periphyton communities, and division of responses between N and P for communities that do show growth in response to enrichment.
        
        In fact, Dodds
        et al. (2002) have given evidence of thresholds
        (P > 30 lg L)1, N>40 lg L)1) above which there
        appears to be a breakpoint to higher chlorophyll.
        
        The second simulation
        (Fig. 9) shows that temperature and length of growing
        season explain a large difference across elevations in
        the expected (simulated) terminal biomass at the end
        of the growing season: 10 times initial biomass at the
        highest elevations versus 1000 times initial biomass at
        the lowest elevations.
    - - Periphyton biomass rarely responded positively to in-situ experimental enrichment with nitrogen or phosphorus. In the summer, nutrient enrichment overall had no effect on periphyton biomass, while outside the growing season N enrichment had inhibitory effects on periphyton.
        4. Despite these experimental results, surveys of ambient chlorophyll a concentrations in streams across the HBEF demonstrated no relationship between streamwater dissolved inorganic N or P concentrations and benthic chlorophyll a.
        5. Our results suggest that HBEF periphyton communities are not closely regulated by nutrient availability, even during periods of high light availability. The inhibitory effects of nutrient enrichment outside the growing season are interesting, but further research is necessary to elucidate the mechanisms driving these responses
    - - We found that if algae showed significant response to nutrient addition, N limitation (either N alone or N with P) was the most frequent response both on GF/F filters and on wood. Despite the low dissolved nutrient concentrations in our study streams, more than a third of the streams did not show any response to N or P addition
    - - Our results indicate that in headwater streams with intact tree canopies, chronic nutrient enrichment at moderate concentrations may have little detectable effect on benthic algal composition or periphyton biomass. Although nutrients stimulated algal growth rates, the long-term effects of nutrient addition on periphyton biomass were small in magnitude compared with other published values and were potentially suppressed by light availability and invertebrate consumption
    - - Analysis of the Maitai River
        data showed that a reduction in DIN was not associated with a
        reduction in Phormidium cover (Wood et al., 2015a).
      - established Phormidium-dominated
        mats are likely to be able to persist under lower than predicted DIN
        concentrations due to nutrient cycling occurring, aided by nitrogen
        fixing bacteria. The synthesis of these field-based studies suggests
        that Phormidium proliferations can occur, or at least initiate, at low
        ambient concentrations of both DRP and DIN. The ability to
        accumulate biomass at low ambient nutrient concentrations and
        accumulate and retain nutrients as they grow is a well described,
        microbial mat trait (Bonilla et al., 2005; Quesada et al., 2008).
      - McAllister et al 2016
        The data collated in this review indicated that only slightly
        elevated water-column DIN concentrations are required for
        Phormidium growth, and that proliferation occurs when water-
        column DRP is low.
  - - - The greatest portion of variance in models for the mean and maximum biomass of benthic stream algae (about 40%) was explained by concentrations of total N and P. Breakpoint regression and a two-dimensional KolmogorovSmirnov statistical technique established significant breakpoints of about 30 µg total P·L1 and 40 µg total N·L1, above which mean chlorophyll values were substantially higher.
    - - A literature review indicates (1) stream benthic chlorophyll is significantly correlated to both total N and total P in the water column, with both nutrients explaining more variance than either considered alone; (2) nutrients have increased substantially in many rivers and streams of the United States over reference conditions, and strong shifts in N and P stoichiometry have occurred as well; (3) bioassays often indicate N responses alone or in concert with P responses for autotrophic (primary production and chlorophyll) and heterotrophic (respiration) responses; (4) both heterotrophic and autotrophic processes are influenced by the availability of N and P; and (5) N-fixing cyanobacteria usually do not seem to be able to fully satisfy N limitations in rivers and streams when P is present in excess of N. These data suggest both N and P control should be considered in the eutrophication management of streams.
      - At least
        for rivers and streams, suspended algae in the water
        column are distinct from benthic algal biomass, with the
        planktonic biomass forming a minor amount of total
        algal biomass in any but the slowest and largest lentic
        systems. This spatial separation of primary productivity
        could be one reason the chlorophyll/nutrient relationships
        are much weaker in streams than in lakes, but other
        factors could increase variability, including flooding
        (e.g., Biggs 1995), herbivory, and light attenuation by
        riparian vegetation.
      - As we demonstrate,
        there is strong evidence that anthropogenic N and P
        enrichment has influenced eutrophication-related water
        quality in fluvial ecosystems.
    - - In a study of modestly impacted streams in the
        foothills and mountains of Colorado, Lewis and
        McCutchan (2010) found no evidence for correlation of
        periphyton biomass correlation with any form of P and a
        weak but significant correlation with dissolved inorganic
        N concentrations. They suggested that greater concentration
        increases could be necessary to increase benthic algal
        biomass; that invertebrate grazing cannot explain their
        observed patterns; and that other factors, such as algal
        biomass at start of growing season, length of growing
        season, and water temperature, explained more of the
        variation of periphyton biomass in these nutrient-poor to
        modestly enriched streams.
    - - Indirect relationship
        
        Niyogi, D.K., Koren, M., Arbuckle, C.J. et al.
        Environmental Management (2007) 39: 213.
        doi:10.1007/s00267-005-0310-3
        
        Algal biomass is usually related to nutrient concentrations, and this was the case for epilithic algae on cobbles in our streams.
        
        However the relationship is complex when sediment deposition resulting from erosion of soil an stream banks is considered
        
        If streams are aggrading in this manner, their smaller substrates might be less stable and accumulate less algae and moss compared to bedrock and boulders in tussock streams (Biggs, 1996; Suren and Duncan, 1999).
        
        Additionally, fine sediment might become entrained in high flows and scour algal biomass during floods (Schofield and others 2004).
      - Cyanobacteria
        
        Wood et al 2016
        10 sites, 7 NZ rivers
        
        Generalized additive mixed models (GAMMs) identified dissolved inorganic N (DIN) over the accrual period <0.8 mg/L, dissolved reactive P accrual <0.005 mg/L, water temperatures >15°C, and conductivity as having positive and statistically significant effects on % Phormidium cover
        
        ie low DIN in growth stage
        had +ve effect
        
        In contrast to planktonic cyanobacterial blooms, Phormidium proliferations generally occur at sites with relatively good water quality (McAllister et al. 2016).
        
        Phormidium, but they contain other organisms including bacteria, other cyanobacteria, and algae, which are jointly adhered to the substrate by extracellular polymeric substances
        
        Heath, M., et al. (2016).
        
        Land-use intensification and urbanization, has led to increased nitrogen and phosphorus concentrations in aquatic systems (Conley et al. 2009). Nitrogen and phosphorus are the major nutrients favouring the development of planktonic cyanobacteria (Rapala and Sivonen 1998). Consequently, the relationship between planktonic cyanobacteria and these nutrients has received significant scientific attention (Paerl 1996; Chorus and Bartrum 1999; Paerl, Hall and Calandrino 2011). In contrast, there is a limited understanding of the interplay between nitrogen, phosphorus and benthic cyanobacterial proliferations in lotic systems. In New Zealand rivers, Phormidium spp. blooms have been associated with elevated nitrogen (ca. >0.1 mg L−1) and low-phosphorus concentrations (c. <0.01 mg L−1; Wood and Young 2011, 2012).
        
        The High Nitrate High Phosphate treatment had the highest cell concentrations and longest exponential growth phase for both P-NT and P-T. In comparison, the two nitrate-reduced treatments had the lowest cell concentrations. In situ observations from New Zealand rivers have shown that the greatest Phormidium cover usually occurs when dissolved inorganic nitrogen (DIN) concentrations are over a threshold of ca. 0.2 mg L−1 (; Heath et al. 2013; Wood et al. 2015
        
        Increasing phosphate concentration in this culture-based study increased cell biomass. In contrast, Phormidium blooms are generally observed in New Zealand rivers with low-phosphate (<0.01 mg L−1; Heath, Wood and Ryan 2011; Wood and Young 2012; Wood et al. 2015). Many cyanobacteria are able to store phosphates as polyphosphates in polyphosphate bodies (also called volutine granules; Kromkamp 1987) which enables them to perform two to four cell divisions, comparable to a 4—32-fold increase in biomass (Mur, Skulberg and Kilen 1999). This may provide this species with a competitive advantage over other cyanobacteria/algae especially during the early growth phase.
        
        batch monocultures experiments The High Nitrate High Phosphate treatment had the highest cell concentrations and longest exponential growth phase for both P-NT and P-T.
        
        Wood et al 2015
        
        Water trapped within the mucilaginous Phormidium mat matrix had on average 320-fold higher DRP concentrations than bulk river water and this, together with elevated concentrations of elements, including iron, suggest phosphorus release from entrapped sediment
        
        If sediment provides a source of phosphorus for Phormidium, a relationship between sedimentation rates and the prevalence of Phormidium proliferations might be expected. This trend was observed by Wood and Bridge [24] who showed a correlation between increased quantity of deposited fine sediment and sites with Phormidium proliferations in the Maitai River (Nelson, New Zealand).
        
        dissolved inorganic nitrogen (DIN) at site A is below 0.2 mg L-1(www.lawa.org.nz), which is the generally accepted concentration required for bloom formation Wood SA, Wagenhoff A, Young R. The effect of flow and nutrients on Phormidium abundance and toxin production in rivers in the Manawatu-Whanganui region. Cawthron Report No. 2575. 2014. 42 p.
        
        Metallic oxide-bound phosphorus, which consists of phosphorus bound to iron and aluminium oxides
    - - For example, nutrient enrichment can affect
        periphyton and bacterial assemblages directly via com-
        petitive release of nutrient limitation
    - - Meta-analysis of lotic nutrient (N and P) amendment experiments indicated that simultaneous stimulation of benthic algal community biomass by .1 nutrient was the rule,
        not the exception. Addition of a limiting nutrient typically doubled algal biomass, whereas addition of another nutrient generally increased algal biomass ;1.25-fold. N was approximately equally likely as P to be limiting.
    - - Only when reference nutrient concentrations are in the upper one third of those expected in the United States, is maximum benthic chlorophyll projected to exceed 100 mg m-2 (a concentration commonly used to indicate nuisance levels) >30% of the time
    - - Increasing nutrients by 60–99% of ambient concentrations increased periphyton percentage cover and biomass. Periphyton abundance also increased with increasing duration of exposure to nutrients (2, 4 and 8 weeks); however, short-term pulses of nutrients (2 weeks) had no significant effect in the rural stream. These results indicate that effective management of nutrient delivery, by reducing time periods of high nutrient load, will minimise impacts to benthic environments.
    - - 4.RDAs showed that industrial organic compounds, herbicides and PhC products were the pollutants most strongly associated with measures of biofilm structure and function, whereas dissolved inorganic nitrogen, dissolved organic carbon and hydrological variability were the environmental factors most strongly associated with biofilm responses
    - - Because reductions in SO2 emissions have reduced the atmospheric deposition of H2SO4 across large portions of North America and Europe, while emissions of NOx have gone unchecked, HNO3 is now playing an increasing role in the acidification of freshwater ecosystems. This acidification process has caused several adverse effects on primary and secondary producers, with significant biotic impoverishments, particularly concerning invertebrates and fishes, in many atmospherically acidified lakes and streams. The cultural eutrophication of freshwater, estuarine, and coastal marine ecosystems can cause ecological and toxicological effects that are either directly or indirectly related to the proliferation of primary producers. Extensive kills of both invertebrates and fishes are probably the most dramatic manifestation of hypoxia (or anoxia) in eutrophic and hypereutrophic aquatic ecosystems with low water turnover rates. The decline in dissolved oxygen concentrations can also promote the formation of reduced compounds, such as hydrogen sulphide, resulting in higher adverse (toxic) effects on aquatic animals. Additionally, the occurrence of toxic algae can significantly contribute to the extensive kills of aquatic animals. Cyanobacteria, dinoflagellates and diatoms appear to be major responsible that may be stimulated by inorganic nitrogen pollution. Among the different inorganic nitrogenous compounds (NH4+, NH3, NO2−, HNO2, NO3−) that aquatic animals can take up directly from the ambient water, unionized ammonia is the most toxic, while ammonium and nitrate ions are the least toxic. In general, seawater animals seem to be more tolerant to the toxicity of inorganic nitrogenous compounds than freshwater animals, probably because of the ameliorating effect of water salinity (sodium, chloride, calcium and other ions) on the tolerance of aquatic animals.
  - - - Periphyton stoichiometry, cotton decay, and cyanobacterial
        cover responded more strongly to annual median DIN
        concentration
    - - For river periphyton in general, Francoeur et al. (1999) found using artificial substrate experiments, that temperature was the most important variable affecting accrual rate. Heath et al. (2011) also suggested that water temperature is an important factor in determining whether Phormidium proliferations were present or absent, based on field observations of greater proliferation during warm, summer months
        
        However, Biggs (2000) concluded that, when the effects of accrual time were allowed for, the best predictors of overall periphyton biomass were inorganic nitrogen and phosphorus concentrations
- - - - A periphyton nutrient response can be
        represented by a curvilinear model that predicts a very strong response to nutrients at low nutrient
        concentrations followed by decreasing responsiveness
        at higher concentrations, but without any indication
        of an asymptote even up to very high concentrations
        (O’Brien et al., 2007
        
        While no definitive mechanistic
        explanation is yet available for this pattern, possibilities
        include replacement of taxa that develop only
        modest biomass per unit area at low nutrient concentrations
        by other taxa that produce more biomass
        accumulation but require high nutrient concentrations.
        
        As shown primarily by use of artificial substrata, the
        periphyton of streams with low nutrient concentrations
        show widely varied responses to nutrients. For
        example, meta-analyses (Dodds & Welch, 2000; Tank
        & Dodds, 2003; Francoeur, 2001) have shown that
        about half of nutrient manipulation experiments
        indicate no response to the addition of phosphorus
        or nitrogen together or separately. Responses to
        nutrients, when they occur, are nearly equally divided
        between separate N or P limitation and colimitation
        by N and P. Responses typically are stronger for the
        addition of the two nutrients together than for either
        nutrient separately (Francoeur, 2001). These response
        patterns are also typical of lakes (Elser, Marzolf &
        Goldman, 1990; Lewis & Wurtsbaugh, 2008), except
        that the phytoplankton of lakes show a stronger
        growth response at low nutrient concentrations.
    - - Periphyton ecology needs more rigorous manipulative experiments, particularly experiments that generate clear relationships between environmental drivers and ecological responses