Seasonal Variability of the Carbon and Nitrogen Isotopic Signature in a Zostera noltei Meadow at the NW Iberian Peninsula

Abstract

Nitrogen (N) and carbon (C) isotopic analyses in seagrasses have been established as effective environmental tracers to assess the anthropogenic influence on seagrass meadows. The aim of this study was to determine the spatial patterns and seasonal variability in the C and N stable isotopic composition of sediments, leaves and epiphytes at a Zostera noltei meadow in an intertidal complex located at the Ría de Vigo (NW Iberian Peninsula) and to explore the mechanisms underlying such variability.Measurements of carbon and nitrogen stable isotopes, morphological features of Z. noltei and the C:N mass ratios were undertaken monthly during an annual seasonal cycle. N recycling between the seagrass and the sediment under its canopy influenced the spatial and seasonal nitrogen isotopic variability in the Z. noltei meadow. The relative contribution of nitrogen stable isotopes both in Z. noltei and the sediments under its canopy showed significant seasonal differences. The seasonal variability observed in carbon and nitrogen stable isotopes and C:N mass ratios of Z. noltei was mainly explained by the physiological mechanisms of carbon and nitrogen uptake and the differential nutrient demand of the plant depending on the growth stage.

A multidisciplinary approach to identify priority areas for the monitoring of a vulnerable family of fishes in Spanish Marine National Parks

“…Surface dissolved nitrogen concentrations (DIN) and isotopic discrimination for δ 15 N in Ría de Vigo are typically higher from October to April, decreasing from May to September [ 60 ]. Hence, higher δ 15 N signatures in spring–summer would be expected [ 78 , 79 ]. The opposite trend would occur in δ 13 C signatures [ 79 ].…”

Anthropogenic Impact on Zostera noltei Seagrass Meadows (NW Iberian Peninsula) Assessed by Carbon and Nitrogen Stable Isotopic Signatures

“…noltei leaves were not acidified. Previous acidification experiments carried out with samples from A Ramallosa (Román et al, 2018), showed that δ 13 C ratios did not show significant differences between acidified (δ 13 C = -14.0 ± 0.5 ‰) and non-acidified (δ 13 C = -14.0 ± 0.7 ‰) Z. noltei samples (p>0.05, n= 5), suggesting that the amount of carbonates attached to these leaves are likely to be negligible. (Sulzman, 2007).…”

“…Since the Z. noltei samples were collected at different seasons, the biological fractionation exerted by the plant and the epiphytes caused by seasonality can alter the isotopic ratios and complicate a straightforward interpretation of the observed isotopic signatures on the basis of anthropogenic nitrogen inputs (Román et al, 2018).…”

Anthropogenic nutrient inputs in the NW Iberian Peninsula estuaries determined by nitrogen and carbon isotopic signatures of Zostera noltei seagrass meadows

“…Indeed, a relevant fraction of the nitrogen present in seagrass meadows is originated by the decay and decomposition of seagrass leaves (Lee et al, 2007). So this recycling process, jointly with the inputs of matter into the meadow, can modulate the δ N in the sediments, partially explaining the observed correlation between δ N in sediments and in Z. noltei (Román et al, 2018).…”