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Estimating the contribution of carnivorous waterbirds to nutrient loading in freshwater habitats

journal contribution
posted on 01.12.2007, 00:00 authored by S Hahn, S Bauer, Marcel KlaassenMarcel Klaassen
1. We estimated nitrogen (N) and phosphorus (P) loading into wetlands by carnivorous waterbirds with alternative physiological models using a food-intake and an excreta-production approach. The models were applied for non-breeding and breeding Dutch inland carnivorous waterbird populations to quantify their contribution to nutrient loading on a landscape scale.

2. Model predictions based on food intake exceeded those based on excretion by 59–62% for N and by 2–36% for P, depending on dietary assumptions. Uncertainty analysis indicated that the intake model was most affected by errors in energy requirement, while the excretion model was dependent on faecal nutrient composition.

3. Per capita loading rate of non-breeders increased with body mass from 0.3–0.8 g N day−1 and 0.15 g P day−1 in little gulls Larus minutus to 4.5–11.5 g N day−1 and 2.1–3.2 g P day−1 in great cormorants Phalacrocorax carbo. For breeding birds, the estimated nutrient loading by a family unit over the entire breeding period ranged between 17.6–443.0 g N and 8.6 g P for little tern Sterna albifrons to 619.6–1755.6 g N and 316.2–498.1 g P for great cormorants.

4. We distinguished between external (i.e. importing) and internal (i.e. recycling) nutrient loading by carnivorous waterbirds. For the Netherlands, average external-loading estimates ranged between 38.1–91.5 tonnes N and 16.7–18.2 tonnes P per year, whilst internal-loading estimates ranged between 53.1–140.5 tonnes N and 25.2–39.2 tonnes P and per year. The average contribution of breeding birds was estimated to be 17% and 32% for external and internal loading respectively. Most important species were black-headed gull Larus ridibundus and mew gull Larus canus for external loading, and great cormorant and grey heron Ardea cinerea for internal loading.

5. On a landscape scale, loading by carnivorous waterbirds was of minor importance for freshwater habitats in the Netherlands with 0.26–0.65 kg N ha−1 a−1 and 0.12–0.16 kg P ha−1 a−1. However, on a local scale, breeding colonies may be responsible for significant P loading.

History

Journal

Freshwater biology

Volume

52

Issue

12

Pagination

2421 - 2433

Publisher

Wiley-Blackwell

Location

Oxford, England

ISSN

0046-5070

eISSN

1365-2427

Language

eng

Publication classification

C1.1 Refereed article in a scholarly journal

Copyright notice

2007, The Authors