Determinants of invertebrate community structure in glacial-melt streams of southeast Tibet

Authors: FAIR, H - Middlebury College; Smiley, Peter - Rocky; LANNO, ROMAN - The Ohio State University

Submitted to: Freshwater Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/10/2021
Publication Date: 6/12/2021
Citation: Fair, H., Smiley, P.C., Lanno, R. 2021. Determinants of invertebrate community structure in glacial-melt streams of southeast Tibet. Freshwater Biology. 66(7):1282-1295. https://doi.org/10.1111/fwb.13716.
DOI: https://doi.org/10.1111/fwb.13716

Interpretive Summary: The current theoretical model of invertebrate-habitat relationships within glacier streams predicts that invertebrate biodiversity and abundance is predominately influenced by water temperature and channel stability. This model is based on scientific findings in Europe and New Zealand. Invertebrate-habitat relationships within glacier streams in Tibet and Asia have not been evaluated and thus it is unknown whether the current theoretical model is applicable to these streams. Our results documented that the best predictors of invertebrate biodiversity and abundance within glacier streams in Tibet were water temperature, conductivity, or turbidity and that biodiversity in sites closest to the glaciers was greater than expected. These findings are novel because they represent the first documentation of invertebrate-habitat relationships in glacier streams in Tibet. Our novel results will be of much interest to scientists working in streams worldwide because they indicate that there is a need to develop a regional version for Tibet and Asia of the current theoretical model of invertebrate-habitat relationships in glacier streams. Our novel results will also be of much interest to those involved with watershed management and conservation of aquatic biodiversity in Tibet and China because they provide information that can be used to predict changes in water quality that will impact invertebrate biodiversity and abundance within glacier streams in Asia. Our results combined with information from other headwater stream studies will also be of interest to state agencies, federal agencies, private consulting companies, and non-profits involved with the management of agricultural headwater streams in the United States because they confirm the importance of water temperature, conductivity, and turbidity as determinants of invertebrate biodiversity and abundance in these small streams.

Technical Abstract: The Milner et al. (2001a) conceptual model of invertebrate community dynamics in glacial-melt headwaters describes predicted longitudinal changes in invertebrate community structure with changing water temperature and channel stability with increasing distance from glaciers. Previous studies conducted in Europe, Greenland, New Zealand, Asia, and South America have supported the predictions of the Milner & Petts conceptual model and contributed to the refinement of the model. However, none have evaluated if the conceptual model fits the invertebrate community dynamics over a full range of distances from the glacier and water temperature conditions within glacial-melt streams in Tibet and surrounding circum-Himalayan mountain ranges. Our objectives were to determine if: 1) water temperature and channel stability were correlated with distance from the glacier; 2) invertebrate diversity, density, and taxa composition trends were influenced by water temperature and channel stability; and 3) water temperature and/or channel stability were better predictors of invertebrate community structure than other habitat factors (distance from glacier, glacier size, glacial index, conductivity, turbidity). We sampled invertebrates and measured water temperature, specific conductivity, turbidity, and associated glacier-related variables (e.g., distance from glacier, glacier size) within 14 sites in three subalpine glacial-melt catchments within southeastern Tibet’s Three Parallel Rivers region Hengduan Mountain Range during 2010, 2011, 2013, and 2015. Our sites encompassed a temperature gradient from the upstream metakryal sites (Tmax<2oC) to the furthest downstream site (Tmax > 10 oC) near the Mekong River. Tmin and in situ water temperatures were positively correlated with distance from the glacier but Pfankuch Channel Stability Index bottom scores were not correlated with distance from the glacier. Five invertebrate response variables (percent Diamesinae, Diamesinae abundance, Nemouridae abundance, and the site scores from the first and second DCA (Detrended Correspondence Analysis) axes of presence/absence data were best explained by in situ water temperature or both in situ water temperature and Pfankuch Channel Stability Index bottom scores as predicted by the Milner et al. (2001a) model. In contrast with the Milner et al. (2001a) model, predictions for invertebrate response variables (taxa richness, density, and the site scores of the first and second DCA axes of relative abundance data) were best explained by either specific conductivity or turbidity. Evaluation of the percent occurrence trends indicated 13 taxa (Nemouridae morphotype 1, Diamesinae, Orthocladiinae, Rhyacophila, Epeorus, Taeniopterygidae, Baetis, Capnia, Nemouridae morphotype 2, Simuliidae, Limnephilidae, Himalopsyche, and Collembola) frequently occurred within samples having in situ water temperatures < 2 oC, which contradicts the Milner et al. (2001a) model prediction of only Diamesinae occurring in the metakryal sites. Our results indicate that trends in invertebrate community response variables and presence/absence trends from monsoonal temperate glacial-melt catchments during the summer glacier melt season are primarily influenced by water temperature, specific conductivity, and turbidity and not by water temperature and channel stability.