Interactions between fine-grained sediment delivery, river bed deposition and salmonid spawning success

Salmonids clean river bed gravels to lay their eggs. However, during the incubation period fine sediment infiltrates the bed. This has been found to limit the success of salmonid spawning, as fine sediment reduces gravel permeability resulting in intra-gravel flow velocities and O2 concentrations decreasing. The success of salmonid spawning is therefore a function of the coincidence of fine sediment delivery and the development of the salmonid eggs. The presence of fine sediment also exerts sub-lethal effects on the rate of egg development with a negative feedback slowing and extending the incubation process meaning the eggs are in the gravels for longer and susceptible to more potential sediment delivery events. The SIDO (Sediment Intrusion and Dissolved Oxygen)- UK model is a physically-based numerical model which simulates the effect of fine sediment deposition on the abiotic characteristics of the salmonid redd, along with the consequences for egg development and survival. This model is used to investigate the interactions and feedbacks between the timing and concentrations of suspended sediment delivery events, and the deposition of fine sediment within the gravel bed, and the consequences of this on the rate of egg development and survival. The model simulations suggest that egg survival is highly sensitive to suspended sediment concentrations, particularly to changes in the supply rate of sand particles. The magnitude, frequency and specific timing of sediment delivery events effects egg survival rates. The modelling framework is also used to investigate the impact of the rate of gravel infilling by sediment. The hypotheses of continual, discrete event and non-linear decline in the rate of infilling are investigated

Regional-scale drivers of groundwater faunal distributions

Freshwater aquifers are a major source of drinking water; they also possess unique assemblages of organisms. However, little is known about the distributional drivers of obligate groundwater organisms at the regional scale. We examine the distribution and composition of stygobiont assemblages in a complex geological setting and explore the relationship between groundwater fauna, hydrogeology and water chemistry. In the study area we grouped similar geologies into five hydrogeological formations (hydro-units) within which habitats for groundwater fauna were broadly similar. We found that the occurrence of stygobionts differed significantly between hydro-units. Stygobionts were significantly less likely to be recorded in mudstone/siltstone and sandstone aquifers compared with carbonate rocks or with igneous/metamorphic rocks. Variance partitioning indicated that the hydro-units explained a greater proportion of the variance (7.52%) in the groundwater community than water chemistry (5.02%). However, much of the variation remained unexplained. The macrofaunal stygobiont species in our study area formed three groups: (1) Niphargus glenniei was recorded in a range of hydro- units but only in the west of the study area. (2) Niphargus kochianus , Niphargus fontanus, Proasellus cavaticus and Crangonyx subterraneus were predominately recorded in carbonate aquifers in the east of the study area. (3) Niphargus aquilex and Microniphargus leruthi, were found throughout the study area and in a range of hydro-units. We hypothesise that physical barriers exist that prevent some stygobiont taxa from colonizing apparently suitable geologies; the low permeability deposits dividing the western and eastern parts of the study area may partly explain the observed distributions

Regional scale drivers of groundwater faunal distributions

Freshwater aquifers are a major source of drinking water; they also possess unique assemblages of organisms. However, little is known about the distributional drivers of obligate groundwater organisms at the regional scale. We examine the distribution and composition of stygobiont assemblages in a complex geological setting and explore the relationship between groundwater fauna, hydrogeology and water chemistry. In the study area we grouped similar geologies into five hydrogeological formations (hydro-units) within which habitats for groundwater fauna were broadly similar. We found that the occurrence of stygobionts differed significantly between hydro-units. Stygobionts were significantly less likely to be recorded in mudstone/siltstone and sandstone aquifers compared with carbonate rocks or with igneous/metamorphic rocks. Variance partitioning indicated that the hydro-units explained a greater proportion of the variance (7.52%) in the groundwater community than water chemistry (5.02%). However, much of the variation remained unexplained. The macrofaunal stygobiont species in our study area formed three groups: (1) Niphargus glenniei was recorded in a range of hydro- units but only in the west of the study area. (2) Niphargus kochianus , Niphargus fontanus, Proasellus cavaticus and Crangonyx subterraneus were predominately recorded in carbonate aquifers in the east of the study area. (3) Niphargus aquilex and Microniphargus leruthi, were found throughout the study area and in a range of hydro-units. We hypothesise that physical barriers exist that prevent some stygobiont taxa from colonizing apparently suitable geologies; the low permeability deposits dividing the western and eastern parts of the study area may partly explain the observed distributions