Study finds nutrients homogenize the biodiversity of lakes

A new study from researchers at Trinity College has found that the addition of nutrients like nitrogen can homogenize the benthic diversity in lakes. Benthic communities in lakes are the organisms that live at the lowest level of bodies of water, as well as those within the upper sediment layers, and include various types of invertebrates. Despite the scientific community’s spotlight on the issue of eutrophication, little is known of the effects of anthropogenic nutrient enrichment on benthic diversity, especially within lakes.

Ian Donahue and fellow researchers acquired data from an Irish lakes database where littoral invertebrates, profundal/sublittoral invertebrates, total phosphorus, total nitrogen, chlorophyll a, and alkalinity were measured from 1996 to 2002. Replicate samples (six) were collected at 25 lakes facilitating a “within-lake scale” analysis, as well as single samples from 40-52 lakes providing an “among-lake scale” analysis.

Multivariate, statistical analyses demonstrated inverse relationships between every measure of lake nutrient enrichment and the diversity of invertebrate assemblages at the within-lake scale.  At the among-lake scale, the composition of invertebrates was also significantly less heterogeneous in nutrient-rich lakes.

This trend was witnessed at all benthic zones with both the littoral and profundal/sublittoral assemblages losing diversity as nutrient concentrations increased in the lake water. The same result held true throughout different lake sizes and connectivities.

Previous studies have suggested that unnatural nutrient additions can affect biota heterogeneity indirectly, by reducing resource availability and modifying habitat structure and food webs. A common effect of nutrient inputs has been increased production in aquatic vegetation that ultimately decomposes and sucks all available dissolved oxygen, leaving no oxygen for any other organism. Direct effects have also been observed due to decreases in the importance of random processes in structuring assemblages.

This study suggests that rapid nutrient input is detrimental to the benthic biodiversity. However this may not necessarily be the case with natural nutrient enhancements. Other studies have demonstrated positive interactions between benthic biota and natural productivity booms associated with nutrients. This is most likely due to the long timescale natural enrichment occurs on, while unnatural nutrient inputs shock the system in a short amount of time.

The authors suggest, “[their] results have profound implications for the conservation and management of global aquatic biodiversity, owing to the primacy of nutrient enrichment as one of the most pervasive anthropogenic impacts on aquatic ecosystems worldwide and because the problem is expected to increase considerably in the coming decades”

--Reviewed by Evyan Borgnis

Donohue, I., Jackson, A., Pusch, M., & Irvine, K. (2009). Nutrient enrichment homogenizes lake benthic assemblages at local and regional scales Ecology, 90 (12), 3470-3477 DOI: 10.1890/09-0415.1