Investigating the causes of reduced dissolved oxygen concentrations in Kickapoo Creek, TX.

Excessive organic matter and nutrients can depress dissolved oxygen concentration (DOC) in streams. The aim of this study was to understand the depressed DOC of Kickapoo Creek in Texas, USA, which is an impaired stream; identify the possible sources causing the depressed DOC and elevated Escherichia coli levels; and identify possible remedial measures. Monthly grab water quality data was monitored for nine stations in the watershed. For three of the nine stations, 24-h DOC was also monitored for a comparison with the minimum and average DOC criteria. Correlational, graphical, spatial, and temporal analyses were carried out for DOC concentration with other water quality variables which have the potential to depress DOC in the stream. The correlational analyses show a weak to moderate correlation for DOC with nutrient and oxygen-demanding substance concentrations present in the stream. However, there are spatial and temporal trends in DOC data that can be attributed to the nutrient influx into the stream. A pattern of increasing nutrient concentrations from upstream to downstream partially explains the decreasing dissolved oxygen (DO) concentrations observed towards the lower reaches. Visual interpretations of riparian vegetation and sediment influx also support the spatial patterns in DO concentrations. The majority of the depressed DOC occurs in the summer months when streamflow is at a minimum. The depressed DOC during summer is partially explained by the increasing daily temperatures for the summer months as revealed by the trend analysis of the daily temperature data from 1981 to 2020 using the modified Mann-Kendall test, Pettitt test, and Sen's slope.

A comparison of genetically and morphometrically identified macroinvertebrate community index scores with implications for aquatic life use attainment.

Measures of aquatic macroinvertebrate communities are often used to characterize water quality and indicate whether waterbodies are meeting management expectations. The accuracy of these measures depends on the skill and experience of the person identifying the macroinvertebrates, and obtaining these measures can be relatively expensive due to the time necessary for identification. Utilizing genetic identification of macroinvertebrate taxa has the potential to reduce the time of sample processing, identify a greater number of taxa, and increase the resolution of identification. We compared Colorado multi-metric index (MMI) scores from seven locations in the Big Thompson River, CO, based on genetic and morphometric identification and estimated the ability of MMI scores based on genetic identification to characterize aquatic life use attainment management thresholds. We found a significant linear relationship (p = 0.002, R2 = 0.87) between MMI scores generated by genetic and morphological identification. MMIs support the following aquatic life use designations as defined by the Colorado Water Quality Control Commission: Impaired < 40, Attaining > 48, and Ambiguous 40-48. These values correspond to MMIs based on genetic identification as Impaired < 20, Attaining > 64, and Ambiguous = 21-63 based on the prediction interval of the regression equation. Our results suggest that using genetically identified macroinvertebrates to estimate MMI scores can provide some degree of certainty regarding aquatic life use designations, and while it may be inappropriate at the current time to entirely replace morphologically based biotic integrity measures with those based on molecular identification, there are opportunities in their use.

High-throughput environmental DNA analysis informs a biological assessment of an urban stream.

There is growing interest in the use of DNA barcoding and metabarcoding approaches to aid biological assessments and monitoring of waterbodies. While biodiversity measured by morphology and by DNA often has been found correlated, few studies have compared DNA data to established measures of impairment such as multimetric pollution tolerance indices used by many bioassessment programs. We incorporated environmental DNA (eDNA) metabarcoding of seston into a rigorous watershed-scale biological assessment of an urban stream to examine the extent to which eDNA richness and diversity patterns were correlated with multimetric indices and ecological impairment status designations. We also evaluated different filtering approaches and taxonomic classifications to identify best practices for environmental assessments. Seston eDNA revealed a wide diversity of eukaryotic taxa but was dominated by diatoms (36%). Differentiation among sites in alpha and beta diversity was greater when operational taxonomic units (OTUs) were classified taxonomically, but coarse resolution taxonomy (kingdom) was more informative than finer resolution taxonomy (family, genus). Correlations of DNA richness and diversity with multimetric indices for fish and macroinvertebrates were generally weak, possibly because Metazoa were not highly represented in our DNA dataset. Nonetheless, sites could be differentiated based on ecological impairment status, with more impaired sites having lower eDNA diversity as measured by the Shannon index, but higher taxonomic richness. Significant environmental drivers of community structure, as inferred from constrained ordination analyses, differed among kingdoms within the eDNA dataset, as well as from fish and macrobenthos, suggesting that eDNA provides novel environmental information. These results suggest that even a simple seston eDNA filtering protocol can provide biodiversity information of value to stream bioassessment programs. The approach bears further investigation as a potentially useful rapid assessment protocol to supplement more intensive field sampling efforts.