Using diatoms to assess human impacts on streams benefits from multiple-habitat sampling

Abstract

Benthic diatoms are important indicators of human impacts on streams. Epilithic diatoms are collected most often for bioassessments, but potentially important ecological information from other habitats could be missed. Within our study region, substrata ranged from 100% rock to 100% sandy silt at 61 sites, leading us to question the appropriateness of sampling solely epilithic surfaces in riffles. We compared two protocols for collecting diatoms:(1) epilithic habitat samples (EHS) within riffles and (2) multi-habitat samples (MHS), which proportionately included different habitats (e.g., riffles and pools) and substrata (e.g., sand, silt, and rock). Three streams were not compared because rocks were absent. Nonmetric multidimensional scaling indicated that diatom communities from EHS and MHS responded similarly to alkalinity and agricultural gradients, and Procrustes analysis showed that ordinations were similar (P \ 0.01). Percent motile diatoms and metrics indicating high or low P and N from MHS showed stronger relationships with land use variables than those metrics from EHS. Bray-Curtis (BC) similarity between the protocols increased as diversity and richness decreased in MHS, as agricultural impacts increased, and as motile diatoms became more abundant in EHS, which likely indicated greater habitat homogeneity or an overriding effect of water chemistry. The two protocols classified 78% of sites concordantly as minimally impacted or impacted. Multi-habitat sampling is preferred where stream habitats vary greatly because it assessed land use impacts more effectively than EHS, while indicating water chemistry impacts as effectively. Multiple habitats also contained greater species diversity, which is important to documenting species distributions, and were always available for sampling, whereas epilithic habitats could be sparse or absent.

Suggestions for diatom-based monitoring in intermittent streams

“…the motile taxa, whose potentialities as physical disturbance indicators have been already recognized. Our observations match with the results obtained by Smucker and Vis (2010) who observed higher percentages of motile diatoms through a multihabitat sampling approach. Motile taxa are linked to depositional habitats and increased siltation: for this reason, they are also considered excellent indicators of anthropogenic impacts and show strong correlations with land use variables (Smucker and Vis, 2010).…”

“…Our observations match with the results obtained by Smucker and Vis (2010) who observed higher percentages of motile diatoms through a multihabitat sampling approach. Motile taxa are linked to depositional habitats and increased siltation: for this reason, they are also considered excellent indicators of anthropogenic impacts and show strong correlations with land use variables (Smucker and Vis, 2010). In Italy, several studies carried out in the Mediterranean hydroecoregions already pointed out the importance to detect the percentage of motile Tab. 3).…”

Environmental and spatial factors drive diatom species distribution in Alpine streams: Implications for biomonitoring

“…priority effects) or individual spillover from upstream populations (i.e. mass effect), the analysis of the functional profile of diatom communities supports the role of dispersal limitation because the motile guild is dominant in impacted sites, which has been observed to be associated with both hydrological (Elias et al 2015;Falasco et al 2016) and morphological (Smucker and Vis, 2010;Bona et al 2016) alterations. Our results therefore suggest that considering diatom response not only to trophic conditions but also to physical alterations is crucial in biomonitoring programs.…”

Contributions of habitat sampling and alkalinity to diatom diversity and distributional patterns in streams: implications for conservation

“…Recently, diatom assessments generated from epilithic habitat and multi-habitat sampling methods have shown similar conclusions or slightly stronger relationships of multihabitat samples with environmental and landuse variables (Winter and Duthie 2000b;Smucker and Vis 2010). In addition, algal communities on hard and soft substrata may indicate similar environmental gradients, although species composition can differ (Cattaneo et al 1997;Potapova and Charles 2005).…”

“…Despite the many variables that interact with habitats, percent EH, which can be affected by human impacts, was a useful proxy that was related to diatom diversity. Beyond effects on diversity, sediment loads attributed to agriculture can cause a subsequent increase in the relative abundance and number of motile and high nutrient diatom species (Bahls et al 1992;Fore and Grafe 2002;Smucker and Vis 2009), which is a relationship that could potentially be missed when only collecting EH samples (Smucker and Vis 2010). Low and high alkalinity reduced or negated the effect of intermediate amounts of EH on diatom diversity, and increased diversity was directly and significantly correlated with greater alkalinity.…”