Habitat, water quality, seasonality, or site? Identifying environmental correlates of the distribution of groundwater biota

Abstract

The distribution of biota in aquatic ecosystems, including aquifers, is collectively influenced by habitat structure, water quality, seasonality, and local variations in environmental conditions. However, little is known about the nature and relative influences of such factors in groundwater ecosystems. Our aims were to identify the key environmental variables influencing the distribution of biota within the Gwydir River alluvial aquifer in northwestern New South Wales, Australia, and to consider the relative importance of environmental variables, in terms of habitat structure, water quality, seasonality, and site attributes, to both microbial and invertebrate (stygofauna) assemblages. Stygofauna distribution was primarily influenced by habitat variables (predominantly sediment structure) followed by site variables (abundance of trees), with water quality and seasonality having relatively little influence. These results indicate that it is the aquifer conditions relating to habitat structure, water flow, and the supply of organic matter that are most important for determining stygofauna distribution. Microbial assemblage structure was not strongly correlated with habitat variables, possibly because habitat restraints do not exist because of their smaller size. Instead, seasonality and water-quality variables had the greatest influence on microbial assemblages. Microbes might respond to seasonal (particularly rainfall induced) changes in water quality more quickly than do stygofauna, which may explain the relatively greater importance of seasonality and water quality to microbial assemblages. Given that stygofauna are most influenced by habitat and site variables, and microbial assemblages are most influenced by seasonality and water quality, disturbance to any of these factors may threaten the stability and integrity of the groundwater ecosystem.

Wells provide a distorted view of life in the aquifer: implications for sampling, monitoring and assessment of groundwater ecosystems

“…Pumping equipment was sterilised between sites (Table 1)89. The sterilisation process, combined with pumping 200 L of well water at each site before sampling, was considered sufficient to remove any contaminants before microbial samples were collected90.…”

“…Stygofauna were collected by pumping 150 L of groundwater into clean buckets and filtering that water through a 63 μm mesh sieve2690. The contents of the sieve were transferred to a sample jar and preserved in ethanol.…”

Groundwater–surface-water interactions: current research directions

“…The environment-community correlations revealed by these studies are very coarse grained. Korbel and Hose (2015) used wells in a single alluvial aquifer in Australia to identify associations between invertebrate and microbial communities and a suite of environmental factors that exhibit small-scale variability (e.g., sediment grain size, water chemistry). The wells were sampled during and after a severe drought to provide additional information about the effects of climatic variation.…”

Groundwater–surface-water interactions: perspectives on the development of the science over the last 20 years

“…For example, seepage through the beds of rivers can recharge large aquifers so that distance from the river may be a primary influence on groundwater chemistry and the distribution of organisms found in these groundwater systems (e.g., Larned et al 2015). Conversely, aquifer recharge may be dominated by precipitation so that spatial patterns in the overlying soils and regional geology may determine the distribution of organisms found in groundwater systems (Johns et al 2015, Korbel andHose 2015). Discharge of long-residence-time ground waters from re- Table 1.…”

“…Studies at the scales of large floodplain aquifers to regional aquifers are difficult because access to these systems requires deep wells. As a consequence, such studies are relatively rare and those published here are mostly descriptive (Johns et al 2015, Korbel and Hose 2015, Larned et al 2015. Several authors in the 2015 special series explored methodological approaches to studying GW-SW interactions (study topic = M or S/M, Table 1).…”