Saffarinia, P. | bioRxiv Science

bioRxiv2022

Aspects of flow variability and spatial context predict temporal beta diversity in river metacommunities

O_LIRiver catchments are dynamic networks that contain multiple levels of spatial and temporal complexity. Benthic macroinvertebrates are key indicator taxa throughout catchments and beta diversity has been used as a metric to explore determinants of community composition at the catchment scale. Commonly explored drivers of beta diversity include environmental and spatial variables such as flow, temperature, and spatial distance. While factors influencing spatial beta diversity have been explored, factors explaining temporal beta diversity have been understudied. Temporal beta diversity is predicted to also be important since community assembly mechanisms are not stable over time, and more studies are needed to determine which factors most strongly determine temporal beta diversity patterns. C_LIO_LIWe investigated the effects of local environmental variables, flow variability, and spatial context on temporal beta-diversity using a large, publicly available biomonitoring dataset from river networks in California. Data included benthic macroinvertebrate community composition and environmental data from multiple locations and years, allowing us to explore temporal changes in these communities as a function of site-specific environmental and spatial factors. Associated gage data were used to calculate hydrograph metrics and contextualize the flow regime at each location over long timescales. We then used beta regression to model the relationship between benthic macroinvertebrate temporal beta-diversity, environmental variables, flow regimes, and spatial network context. C_LIO_LIFlow and spatial catchment-related predictors were the strongest predictors of temporal beta diversity, while changes in environmental variables were much weaker. Channel slope, drainage density, and upstream catchment area were the most significant spatial factors. Channel slope showed a negative relationship with temporal beta diversity, while drainage density and upstream catchment area showed positive ones. Temporal beta diversity was also higher when the rate and magnitude of rises and falls in flow was higher in the hydrograph as well as when the number of zero-flow days and the duration of flow rises and falls was higher. C_LIO_LIOverall, our results indicate that temporal beta diversity of freshwater benthic macroinvertebrates is shaped by both long-term hydrological context and spatial context, and that these factors may serve as better predictors of long term community variability than variability in point estimates of environmental measurements. Flow regimes and spatial metrics may provide more environmental context than point-estimate environmental measurements, as the latter may not accurately capture the dynamic conditions that drive variability in metacommunity responses. C_LIO_LIOur study supports the need for biomonitoring efforts at long spatial and temporal timescales, and highlights the need to consider metacommunity change in the management of freshwater systems. C_LI

ecology↗

bioRxiv2020

Reconciling fish and farms: Methods for managing California rice fields as salmon habitat

The rearing habitat for juvenile Chinook Salmon (Oncorhynchus tshawytscha) in California, the southernmost portion of their range, has drastically declined throughout the past century. Recently, through cooperative agreements with diverse stakeholders, winter-flooded agricultural rice fields in Californias Central Valley have emerged as promising habitat for rearing juvenile Chinook Salmon. From 2013 to 2016, we conducted a series of experiments examining methods for rearing fall-run Chinook Salmon on winter-flooded rice fields in the Yolo Bypass, a modified floodplain of the Sacramento River in California. These included: 1) influence of field substrate differences from previous season rice harvest; 2) effects of depth refugia from avian predators (trenches); 3) field drainage methods to promote efficient egress of fish; and 4) in-field salmon survivorship over time. Zooplankton (fish food) in the winter-flooded rice fields were 53-150x more abundant when directly compared to the adjacent Sacramento River. Correspondingly, somatic growth rates of juvenile hatchery-sourced fall-run Chinook Salmon stocked in rice fields were two to five times greater versus fish in the adjacent Sacramento River. Post-harvest field substrate treatments had little effect on the lower trophic food web and had an insignificant effect on growth rates of in-field salmon. Though depth refugia did not directly increase survival, it buffered maximum water temperatures in the trenches and facilitated outmigration from fields during draining. Rapid field drainage methods yielded the highest survival and were preferable to drawn-out drainage methods. High initial mortality immediately after stocking was observed in the survival over time experiment with stable and high survival after the first week. In-field survival ranged 7.4-61.6% and increased over the course of the experiments. Despite coinciding with the most extreme drought in Californias recorded history, which elevated water temperatures and reduced the regional extent of adjacent flooded habitats which concentrated avian predators, the adaptive research framework enabled incremental improvements in design to increase survival. The abundance of food resources and exceptionally high growth rates observed during these experiments illustrate the benefits associated with reconciling off-season agricultural land use with fish conservation practices. Without any detriment to flood control or agricultural yield, there is great promise for reconciliation ecology between agricultural floodplains and endangered fish conservation where minor alterations to farm management practices could greatly enhance the effectiveness of fish conservation outcomes.

ecology↗

bioRxiv2020

Reconciling fish and farms: Methods for managing California rice fields as salmon habitat

The rearing habitat for juvenile Chinook Salmon (Oncorhynchus tshawytscha) in California, the southernmost portion of their range, has drastically declined throughout the past century. Recently, through cooperative agreements with diverse stakeholders, winter-flooded agricultural rice fields in Californias Central Valley have emerged as promising habitat for rearing juvenile Chinook Salmon. From 2013 to 2016, we conducted a series of experiments examining methods for rearing fall-run Chinook Salmon on winter-flooded rice fields in the Yolo Bypass, a modified floodplain of the Sacramento River in California. These included: 1) influence of field substrate differences from previous season rice harvest; 2) effects of depth refugia from avian predators (trenches); 3) field drainage methods to promote efficient egress of fish; and 4) in-field salmon survivorship over time. Zooplankton (fish food) in the winter-flooded rice fields were 53-150x more abundant when directly compared to the adjacent Sacramento River. Correspondingly, somatic growth rates of juvenile hatchery-sourced fall-run Chinook Salmon stocked in rice fields were two to five times greater versus fish in the adjacent Sacramento River. Post-harvest field substrate treatments had little effect on the lower trophic food web and had an insignificant effect on growth rates of in-field salmon. Though depth refugia did not directly increase survival, it buffered maximum water temperatures in the trenches and facilitated outmigration from fields during draining. Rapid field drainage methods yielded the highest survival and were preferable to drawn-out drainage methods. High initial mortality immediately after stocking was observed in the survival over time experiment with stable and high survival after the first week. In-field survival ranged 7.4-61.6% and increased over the course of the experiments. Despite coinciding with the most extreme drought in Californias recorded history, which elevated water temperatures and reduced the regional extent of adjacent flooded habitats which concentrated avian predators, the adaptive research framework enabled incremental improvements in design to increase survival. The abundance of food resources and exceptionally high growth rates observed during these experiments illustrate the benefits associated with reconciling off-season agricultural land use with fish conservation practices. Without any detriment to flood control or agricultural yield, there is great promise for reconciliation ecology between agricultural floodplains and endangered fish conservation where minor alterations to farm management practices could greatly enhance the effectiveness of fish conservation outcomes.

ecology↗