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

TRFLP profiles at TFM for (A) planktonic bacteria (B) particle associated bacteria.

<p>Non-Metric Multidimensional Scaling (NMDS) plot with solid lines illustrating the interval, but not statistical significance.</p

Grouped summary chemistry results.

<p>A) pH, B) DO, C) SEC, D)Cl, E)Ca, F)TP, G)TDP, H)PP, I)SRP, J)DHP, K) N:P(molar), L)DOC, M)NO₃, N)Fe and O)Zn. Box = interquartile range, horizontal bar = median value, range of whiskers = ±1.5x interquartile range, outlier values are displayed = values that fall outside the range of whiskers. P values calculated using Kruskal-Wallis test. Wilcoxon rank tests were used to investigate differences between two pairs of groups, significance denoted as follow: **0.01, *0.05, ^▪0.1.</p

Borehole study sites.

<p>Notes: BH is borehole; m aod is metres above sea level; m bd is metres below datum; datum is ground level at BPW and top of casing at TFM; water level (WL) range from continuous data between January 2003 and March 2012.</p

Bacteria counts by flow cytometry in intervals (A) BPW and (B) TFM.

<p>Bacteria counts by flow cytometry in intervals (A) BPW and (B) TFM.</p

Theoretical maximum velocities with distance away from a borehole in different flow systems.

<p>Assuming a 150 mm diameter borehole, a 2.1 m length test interval, a pumping rate of 1.79 L/sec, and a total of 5 m³ is abstracted.</p

Cumulative Niphargidae captured with volume abstracted from each interval (A) BPW (B) TFM.

<p>Cumulative Niphargidae captured with volume abstracted from each interval (A) BPW (B) TFM.</p

Unwrapped 360° optical images of packer intervals with horizontal exaggeration of X10.

<p>RWL is rest water level; m bd is metres below datum; datum is ground level at BPW and top of casing at TFM.</p

Theoretical sampled distances from boreholes for different flow systems assuming an interval length of 2.1 m.

<p>Theoretical sampled distances from boreholes for different flow systems assuming an interval length of 2.1 m.</p