Climate warming and agricultural stressors interact to determine stream macroinvertebrate community dynamics

Abstract

Global climate change is likely to modify the ecological consequences of currently acting stressors, but potentially important interactions between climate warming and land-use related stressors remain largely unknown. Agriculture affects streams and rivers worldwide, including via nutrient enrichment and increased fine sediment input. We manipulated nutrients (simulating agricultural run-off) and deposited fine sediment (simulating agricultural erosion) (two levels each) and water temperature (eight levels, 0-6°C above ambient) simultaneously in 128 streamside mesocosms to determine the individual and combined effects of the three stressors on macroinvertebrate community dynamics (community composition and body size structure of benthic, drift and insect emergence assemblages). All three stressors had pervasive individual effects, but in combination often produced additive or antagonistic outcomes. Changes in benthic community composition showed a complex interplay among habitat quality (with or without sediment), resource availability (with or without nutrient enrichment) and the behavioural/physiological tendency to drift or emerge as temperature rose. The presence of sediment and raised temperature both resulted in a community of smaller organisms. Deposited fine sediment strongly increased the propensity to drift. Stressor effects were most prominent in the benthic assemblage, frequently reflected by opposite patterns in individuals quitting the benthos (in terms of their propensity to drift or emerge). Of particular importance is that community measures of stream health routinely used around the world (taxon richness, EPT richness and diversity) all showed complex three-way interactions, with either a consistently stronger temperature response or a reversal of its direction when one or both agricultural stressors were also in operation. The negative effects of added fine sediment, which were often stronger at raised temperatures, suggest that streams already impacted by high sediment loads may be further degraded under a warming climate. However, the degree to which this will occur may also depend on in-stream nutrient conditions.

Organic sediment pulses impact rivers across multiple levels of ecological organization

“…Many headwater rivers are increasingly affected by sedimentation, including those draining peatland catchments, yet experimental studies examining the effect of organic sediment influx on populations, community structure, and functional processes in these river ecosystems remain scarce (Piggott, Lange, Townsend, & Matthaei, ; Piggott et al, ). Our experiment in two peatland rivers revealed that organic sediment influx can have immediate impacts on river water quality and across different levels of biological organisation (macroinvertebrate behavioural drift and whole river metabolism).…”

“…Sedimentation is a major cause of ecological degradation in freshwater ecosystems, with artificially enhanced delivery and retention of fine sediments in rivers and lakes now a significant global problem (Dudgeon et al, ; Larsen & Ormerod, ; Piggott, Townsend, & Matthaei, ; Wood & Armitage, ). A range of policy mechanisms related to the protection of the water environment and wildlife require a better understanding of the scale, nature, and mechanisms of impact so that informed management strategies can be developed and implemented.…”

Predicting Impact of Climate Change on Water Temperature and Dissolved Oxygen in Tropical Rivers

“…In the former, it will reduce water temperature and increase the DO concentration. Thus, multiple stressors and climate change might change the prediction level of river water temperature and DO concentration in an agricultural dominated catchment [63]. However, in our case, we considered the conventional agricultural practices only in the study area and their impact are not considered in our scope of studies.…”

Importance of Riparian Zone: Effects of Resource Availability at Land-water Interface

“…However, total aquatic insect emergence biomass was not influenced by warming, and thus caused an average larger individuals emerging from warm waterbodies [127]. Conversely, another study showed that only the emerging Chironomidae adults were larger with raised temperature, while the emergence of both medium and large-sized insects were decreased, moreover, rising temperature decreased time to emergence [128]. Warming also increased 38% biomass of overall insect emergence, and advanced the spring pulses of aquatic emergence, and this effect was stronger in the presence of fish [129].…”