Freshwater invertebrate responses to fine sediment stress: a multi-continent perspective

Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand, and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, i.e., taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed greater tolerance with most compositional change occurring between 30-60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles

Multiple-stressor effects along gradients of deposited fine sediment and dissolved nutrients in streams

Ecological degradation of streams and rivers as a result of agricultural land-use intensification is a major concern in New Zealand and other parts of the world. Agriculture introduces multiple stressors to streams, presenting a challenge for freshwater managers who must understand the relative strengths of each individual stressor and their combined multiple-stressor effects if they are to implement the most effective management actions and avoid ‘ecological surprises’ that arise from complex interactions between stressors. To investigate patterns of ecological response variables across broad gradients of two major stressors, augmented levels of dissolved inorganic nutrients and deposited fine sediment, I designed a streamside mesocosm experiment with eight levels each of nutrients (36 to 6900 micrograms per litre of dissolved inorganic nitrogen plus 1.4 to 450 micrograms per litre of dissolved reactive phosphorus) and deposited fine sediment (0 to 100 % cover of the streambed), and conducted a field survey in a regional set of 43 streams ranging from 2nd to 6th order. I used multiple linear regression and an information-theoretic approach to select the best predictive models for a series of ecological response variables, including algal, invertebrate and ecosystem variables, and tested (1) the subsidy-stress hypothesis for each stressor (where at low stressor levels an ecological variable responds positively until an inflection point beyond which the effect is negative), (2) whether sediment and nutrients operated as single or multiple stressors and whether they interacted with each other, and (3) whether sediment effects were more pervasive than those of augmented nutrient concentrations. In the 21-day long experiment, subsidy-stress patterns across the nutrient gradient were frequently found for algal and invertebrate taxa and communities, but consistently negative response shapes were more prevalent across the sediment gradient. The subsidy-stress hypothesis was not supported by the response of an ecosystem variable (organic matter breakdown, measured using cotton strips and fresh mahoe leaves). Overall, nutrients and fine sediment acted predominantly as multiple stressors and sometimes in complex interactive ways. The relative strengths of fine sediment and nutrient effects were similar for algal response variables but sediment was the more pervasive stressor for invertebrates, a finding that was also supported by the field survey. My field survey further suggested that nutrients and sediment commonly interact in synergistic ways to affect invertebrate variables, with fine sediment overwhelming any subsidy effects that nutrients may have in isolation. The combined experimental and survey results indicate that augmented levels of fine sediment and dissolved inorganic nutrient concentrations need to be managed together because they mostly act as multiple stressors in their effects on algal, invertebrate and ecosystem response variables. While managers should seek to control both nutrient and fine sediment inputs to streams to achieve good ecological stream condition, measures to reduce or avoid further sedimentation are particularly likely to be effective in mitigating ecological impairment and preventing further harm. Finally, in order to best assess the likely causes of decline in stream health, it will be highly desirable for managers to routinely monitor both nutrients (as currently done) and fine sediment in the future

Multiple-stressor effects along gradients of deposited fine sediment and dissolved nutrients in streams

Ecological degradation of streams and rivers as a result of agricultural land-use intensification is a major concern in New Zealand and other parts of the world. Agriculture introduces multiple stressors to streams, presenting a challenge for freshwater managers who must understand the relative strengths of each individual stressor and their combined multiple-stressor effects if they are to implement the most effective management actions and avoid ‘ecological surprises’ that arise from complex interactions between stressors. To investigate patterns of ecological response variables across broad gradients of two major stressors, augmented levels of dissolved inorganic nutrients and deposited fine sediment, I designed a streamside mesocosm experiment with eight levels each of nutrients (36 to 6900 micrograms per litre of dissolved inorganic nitrogen plus 1.4 to 450 micrograms per litre of dissolved reactive phosphorus) and deposited fine sediment (0 to 100 % cover of the streambed), and conducted a field survey in a regional set of 43 streams ranging from 2nd to 6th order. I used multiple linear regression and an information-theoretic approach to select the best predictive models for a series of ecological response variables, including algal, invertebrate and ecosystem variables, and tested (1) the subsidy-stress hypothesis for each stressor (where at low stressor levels an ecological variable responds positively until an inflection point beyond which the effect is negative), (2) whether sediment and nutrients operated as single or multiple stressors and whether they interacted with each other, and (3) whether sediment effects were more pervasive than those of augmented nutrient concentrations. In the 21-day long experiment, subsidy-stress patterns across the nutrient gradient were frequently found for algal and invertebrate taxa and communities, but consistently negative response shapes were more prevalent across the sediment gradient. The subsidy-stress hypothesis was not supported by the response of an ecosystem variable (organic matter breakdown, measured using cotton strips and fresh mahoe leaves). Overall, nutrients and fine sediment acted predominantly as multiple stressors and sometimes in complex interactive ways. The relative strengths of fine sediment and nutrient effects were similar for algal response variables but sediment was the more pervasive stressor for invertebrates, a finding that was also supported by the field survey. My field survey further suggested that nutrients and sediment commonly interact in synergistic ways to affect invertebrate variables, with fine sediment overwhelming any subsidy effects that nutrients may have in isolation. The combined experimental and survey results indicate that augmented levels of fine sediment and dissolved inorganic nutrient concentrations need to be managed together because they mostly act as multiple stressors in their effects on algal, invertebrate and ecosystem response variables. While managers should seek to control both nutrient and fine sediment inputs to streams to achieve good ecological stream condition, measures to reduce or avoid further sedimentation are particularly likely to be effective in mitigating ecological impairment and preventing further harm. Finally, in order to best assess the likely causes of decline in stream health, it will be highly desirable for managers to routinely monitor both nutrients (as currently done) and fine sediment in the future

Effect of river flow, temperature, and water chemistry on proliferations of the benthic anatoxin-producing cyanobacterium Phormidium

Proliferations of the benthic anatoxin-producing cyanobacterium Phormidium are increasing in prevalence in cobble-bed rivers worldwide. This proliferation is of particular concern when rivers are used as sources of drinking water or for recreation. Little is known about the physicochemical variables promoting proliferations, and our existing knowledge is based on data from only a few rivers. We assessed Phormidium cover, physicochemical variables, and anatoxin concentrations at 10 sites in 7 New Zealand rivers every week for 2 y. Generalized additive mixed models (GAMMs) identified dissolved inorganic N (DIN) over the accrual period 15°C, and conductivity as having positive and statistically significant effects on % Phormidium cover. Flow intensity, expressed relative to the long-term median, had a positive effect up to 0.4× the median flow and a negative effect when >0.5× the median flow. Quantile regression models showed marked variability among sites in relation to the flow intensity required to reduce % Phormidium cover (90ᵗʰ percentile ranged 0.65–249× the long-term median flow). Anatoxins were detected in variable concentrations in samples from 7 of the 10 sites. GAMMs identified strong relationships between elevated toxin concentrations and low conductivity and increasing % Phormidium cover, and significantly lower toxin concentrations when DIN was <0.2 mg/L. These data demonstrate that multiple physicochemical variables influence Phormidium proliferations and toxin concentrations and indicate that the relative importance of these variables differs among rivers and sites

Paired visual fine sediment (<2mm) data and macroinvertebrate samples from Australia, Brazil, New Zealand and UK

Data provided represents harmonized macroinvertebrate data collected from 3-minute kick and Surber (in the case of some New Zealand data) samples paired with visual fine sediment (Article abstractExcessive fine sediment (particles © the authors, CC-BY-NC 4.0</p

Freshwater invertebrate responses to fine sediment stress: a multi‐continent perspective

Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.</p

Supplementary information files for Freshwater invertebrate responses to fine sediment stress: a multi‐continent perspective

© the authors, CC-BY 4.0Supplemental files for article Freshwater invertebrate responses to fine sediment stress: a multi‐continent perspectiveExcessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.</p

Freshwater invertebrate responses to fine sediment stress: a multi‐continent perspective

Excessive fine sediment (particles <2 mm) deposition in freshwater systems is a pervasive stressor worldwide. However, understanding of ecological response to excess fine sediment in river systems at the global scale is limited. Here, we aim to address whether there is a consistent response to increasing levels of deposited fine sediment by freshwater invertebrates across multiple geographic regions (Australia, Brazil, New Zealand and the UK). Results indicate ecological responses are not globally consistent and are instead dependent on both the region and the facet of invertebrate diversity considered, that is, taxonomic or functional trait structure. Invertebrate communities of Australia were most sensitive to deposited fine sediment, with the greatest rate of change in communities occurring when fine sediment cover was low (below 25% of the reach). Communities in the UK displayed a greater tolerance with most compositional change occurring between 30% and 60% cover. In both New Zealand and Brazil, which included the most heavily sedimented sampled streams, the communities were more tolerant or demonstrated ambiguous responses, likely due to historic environmental filtering of invertebrate communities. We conclude that ecological responses to fine sediment are not generalisable globally and are dependent on landscape filters with regional context and historic land management playing important roles.</p