| 1. |
- Liess, Antonia, et al.
(författare)
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Landuse intensity in stream catchments affects the benthic food web : consequences for nutrient supply, periphyton C:nutrient ratios, and invertebrate richness and abundance
- 2012
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Ingår i: Freshwater Science. - : University of Chicago Press. - 2161-9549 .- 2161-9565. ; 31:3, s. 813-824
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Tidskriftsartikel (refereegranskat)abstract
- Anthropogenic nutrient enrichment increases the supply ratio of N and P to aquatic ecosystems and can affect the identity of the limiting nutrient. Here we focus on how stream communities change along gradients of N and P supply and stream catchment landuse intensity. We used a survey approach in 41 southern New Zealand tributaries to investigate how much changes in water N and P concentrations are reflected in periphyton C:nutrient ratios (C:N or C:P) and how much food quality (high food quality corresponds to low periphyton C:nutrient) is reflected in the abundance and taxonomic richness of benthic invertebrate primary and secondary consumers. We measured streamwater nutrient state, periphyton nutrient ratios, biomass (as chlorophyll a in mu g/cm(2)), algal taxon richness, and macroinvertebrate abundance, taxonomic composition, and richness. We also estimated stream habitat and catchment characteristics, such as current velocity, shading, substrate, geology, and landuse intensity. We calculated the Akaike information criterion (AIC) for each possible multiple linear regression model to select the best predictive models for each response variable. C:nutrient ratios were more strongly negatively related to water-column N than P availability. Neither N nor P availability covaried with periphyton biomass. Lower periphyton C:N partly explained higher grazer, but not predator, abundance. Increased % runoff from pasture and periphyton N:P co-occurred with a decrease in invertebrate taxon richness. For example, a 4x increase in periphyton N:P was related to the loss of similar to 1/2 of invertebrate species, but with high uncertainty (R-2 = 0.13). We conclude landuse intensity affects these southern New Zealand streams, and these effects are mediated by agricultural N runoff into streams (among other factors). Further shifts toward high-intensity farming within stream catchments may lead to losses of benthic species at all trophic levels.
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| 2. |
- Wagenhoff, Annika, et al.
(författare)
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Thresholds in ecosystem structural and functional responses to agricultural stressors can inform limit setting in streams
- 2017
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Ingår i: Freshwater Science. - : University of Chicago Press. - 2161-9549 .- 2161-9565. ; 36:1, s. 178-194
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Tidskriftsartikel (refereegranskat)abstract
- Setting numeric in-stream objectives (limits, criteria) to inform limits on catchment loads for major land use stressors is a promising policy instrument to prevent ecosystem degradation. Management objectives can be informed by thresholds identified from stressor response shapes of ecological indicators based on field survey data. Use of multiple structural and functional indicators and different organism groups provides multiple lines of evidence to make objectives more robust. We measured a suite of ecological indicators during a regional field survey in New Zealand. We built flexible boosted regression tree (BRT) models with a predictor set consisting of nutrient, sediment, and environmental variables and investigated the fitted functions for different types of thresholds across each stressor gradient. Congruence of impact initiation (II) thresholds for N among macroinvertebrate metrics and 2 periphyton indicators provided multiple lines of evidence for ecosystem change with small increases in N concentrations above background levels. Impact cessation (IC) on macroinvertebrate metrics at total N = 0.5 mg/L (below N concentrations that saturate important ecosystem processes) highlighted sensitivity of macroinvertebrate communities to eutrophication. We found few stressor response relationships for sediment. We suggest use of sediment-specific macroinvertebrate metrics and a reliable measure of deposited fine sediment in the future. Few indicators responded to phosphorus (P) concentration. Limited information for setting P objectives highlights the need to develop alternative indicators of P loading. Statistical analysis based on single-stressor inferential threshold models suggested that these models carry high risk of identifying spurious thresholds and are less suitable for setting management objectives. II and IC thresholds of multiple ecological indicators can be used to set robust objectives aimed at different levels of protection of ecosystem health.
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