Carbon and Nitrogen Isotopic Signatures of Zooplankton Taxa in Five Small Subalpine Lakes along a Trophic Gradient

Michela Mazzoni,Emanuela Boggio,Roberta Piscia,Roberta Bettinetti,Marina Manca

doi:10.3390/w10010094

Michela Mazzoni, Emanuela Boggio + Show 3 more

Open Access

https://doi.org/10.3390/w10010094

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Journal: Water	Publication Date: Jan 22, 2018
Citations: 5	License type: CC BY 4.0

Affiliation: University of Insubria, Institute of Ecosystem Study

Abstract

Interest in Stable Isotopes Analyses (SIA) is increasing in freshwater ecology to better clarify ecosystems’ functioning. By measuring carbon and nitrogen isotopic signatures, food sources and organism trophic levels can be tracked, providing quantitative estimates of bi-dimensional niches. In order to describe some general patterns of carbon and nitrogen stable isotope signatures in lakes, we applied SIA to zooplankton community in five subalpine lakes sampled in spring and summer along a trophic gradient (from oligotrophy to hypereutrophy). Within zooplankton taxa, temporal variation in food sources and trophic levels were compared to find out taxon-specific patterns. Carbon and nitrogen isotopic signatures differed among the five lakes, reflecting depth, topography, and trophic status of the lakes. Carbon isotopic signatures varied more considerably in deeper and larger lakes (Mergozzo and Pusiano) than in a shallower and smaller lake (Lake Endine). Nitrogen isotopic signatures were generally more enriched in lakes Pusiano and Moro than in Lake Mergozzo, whereas in summer, they were depleted in all lakes. These observations indicate that zooplankton taxa specific trophic roles differed among lakes and in time.

Highlights

Stable isotopes are increasingly used in aquatic ecological studies to clarify food web functioning by quantifying carbon and nitrogen flows through water ecosystems [1]
In order to describe some general patterns of carbon and nitrogen stable isotope signatures in lakes, we applied Stable Isotopes Analyses (SIA) to zooplankton community in five subalpine lakes sampled in spring and summer along a trophic gradient
Stable carbon isotope ratio (δ13 C‰) reflects the input of carbon revealing the contributions of different food sources, and nitrogen isotope (δ15 N‰) indicates the trophic role because a consumer is typically enriched with respect to its diet (e.g., [5,6,7,8])

Summary

Introduction

Stable isotopes are increasingly used in aquatic ecological studies to clarify food web functioning by quantifying carbon and nitrogen flows through water ecosystems [1]. The basic idea is that the isotope ratio of a consumer depends on its diet. Stable carbon isotope ratio (δ13 C‰) reflects the input of carbon revealing the contributions of different food sources, and nitrogen isotope (δ15 N‰) indicates the trophic role because a consumer is typically enriched with respect to its diet (e.g., [5,6,7,8]). Increasing δ15 N enrichment is usually observed with the increasing lake trophic status [9,10,11]. Carbon contents of planktonic grazers and their food sources differ in response to trophic status in lakes, mainly because of differences in contribution of phytoplankton to the food sources [10]. Less to more 13 C-depleted carbon signatures from littoral to pelagic carbon sources are observed (e.g., [6,12])

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Conclusion