Fish disturbance affects sediment resuspension and biogeochemistry

Background/Question/Methods Sediment resuspension can alter ecological and biogeochemical processes in aquatic systems. For instance, resuspended sediments can reduce light availability to primary producers. Additionally, resuspended sediment organic matter may be remineralized by aerobic microbes. In turn, this may affect inorganic nutrient availability to primary producers. The degree to which sediments are resuspended can depend on many factors including whether the sediments were disturbed prior to a resuspension event. Using an experimental mesocosm system we evaluated the effects of sediment disturbance identity on sediment metabolism and stoichiometry before and after a resuspension event. We varied sediment disturbance over four levels, as the sediments were undisturbed, manually punctured (2% of the surface area), or exposed to fish (either bluegill or catfish). The treatments were applied for several days before the water velocity in the tanks was increased to create a resuspension event.

Results/Conclusions We found that water column chlorophyll concentrations (µg L^-1) were highest in the catfish treatment, both before and after the resuspension event. The concentration of total suspended solids (TSS) was initially higher in the fish (bluegill and catfish) treatments; these differences were not evident after the resuspension event. The carbon to nitrogen (C:N) ratio of the TSS was not affected by disturbance identity but was higher after the resuspension event. The TSS nitrogen to phosphorus (N:P) ratio was highest in the control treatment before the resuspension event. However, there was no difference in the TSS N:P after the water velocity was increased. In addition to altering TSS quality, the resuspension event strongly affected sediment respiration and metabolism. Overall, our results suggest that disturbance and fish species identity can affect the quantity and quality of particulates in the water column. However, the magnitude of these differences may be reduced by resupension events.