The regional and global significance of nitrogen removal in lakes and reservoirs

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Biogeochemistry 93 (2009): 143-157, doi:10.1007/s10533-008-9272-x.Human activities have greatly increased the transport of biologically available N through watersheds to potentially sensitive coastal ecosystems. Lentic water bodies (lakes and reservoirs) have the potential to act as important sinks for this reactive N as it is transported across the landscape because they offer ideal conditions for N burial in sediments or permanent loss via denitrification. However, the patterns and controls on lentic N removal have not been explored in great detail at large regional to global scales. In this paper we describe, evaluate, and apply a new, spatially explicit, annual-scale, global model of lentic N removal called NiRReLa (Nitrogen Retention in Reservoirs and Lakes). The NiRReLa model incorporates small lakes and reservoirs than have been included in previous global analyses, and also allows for separate treatment and analysis of reservoirs and natural lakes. Model runs for the mid-1990s indicate that lentic systems are indeed important sinks for N and are conservatively estimated to remove 19.7 Tg N yr-1 from watersheds globally. Small lakes (< 50 km2) were critical in the analysis, retaining almost half (9.3 Tg N yr-1) of the global total. In model runs, capacity of lakes and reservoirs to remove watershed N varied substantially (0-100%) both as a function of climate and the density of lentic systems. Although reservoirs occupy just 6% of the global lentic surface area, we estimate they retain approximately 33% of the total N removed by lentic systems, due to a combination of higher drainage ratios (catchment surface area : lake or reservoir surface area), higher apparent settling velocities for N, and greater N loading rates in reservoirs than in lakes. Finally, a sensitivity analysis of NiRReLa suggests that, on-average, N removal within lentic systems will respond more strongly to changes in land use and N loading than to changes in climate at the global scale.The NSF26 Research Coordination Network on denitrification for support for collaboration (award number DEB0443439 to S.P. Seitzinger and E.A. Davidson). This project was also supported by grants to J.A. Harrison from California Sea Grant (award number RSF8) and from the U.S. Geological Survey 104b program and R. Maranger (FQRNT Strategic Professor)

Temporal Asynchrony of Trophic Status Between Mainstream and Tributary Bay Within a Giant Dendritic Reservoir: The Role of Local-Scale Regulators

Limnologists have regarded temporal coherence (synchrony) as a powerful tool for identifying the relative importance of local-scale regulators and regional climatic drivers on lake ecosystems. Limnological studies on Asian reservoirs have emphasized that climate and hydrology under the influences of monsoon are dominant factors regulating seasonal patterns of lake trophic status; yet, little is known of synchrony or asynchrony of trophic status in the single reservoir ecosystem. Based on monthly monitoring data of chlorophyll a, transparency, nutrients, and nonvolatile suspended solids (NVSS) during 1-year period, the present study evaluated temporal coherence to test whether local-scale regulators disturb the seasonal dynamics of trophic state indices (TSI) in a giant dendritic reservoir, China (Three Gorges Reservoir, TGR). Reservoir-wide coherences for TSICHL, TSISD, and TSITP showed dramatic variations over spatial scale, indicating temporal asynchrony of trophic status. Following the concept of TSI differences, algal productivity in the mainstream of TGR and Xiangxi Bay except the upstream of the bay were always limited by nonalgal turbidity (TSICHL−TSISD <0) rather than nitrogen and phosphorus (TSICHL−TSITN <0 and TSICHL−TSITP <0). The coherence analysis for TSI differences showed that local processes of Xiangxi Bay were the main responsible for local asynchrony of nonalgal turbidity limitation levels. Regression analysis further proved that local temporal asynchrony for TSISD and nonalgal turbidity limitation levels were regulated by local dynamics of NVSS, rather than geographical distance. The implications of the present study are to emphasize that the results of trophic status obtained from a single environment (reservoir mainstream) cannot be extrapolated to other environments (tributary bay) in a way that would allow its use as a sentinel site

Réponses du zooplancton lacustre aux feux et aux coupes de forêt dans l'écozone boréale du Québec : étude préliminaire

Les changements du zooplancton lacustre à la suite des feux et des coupes à blanc dans la forêt boréale ont été évalués en 1996 en comparant trois groupes de lacs du Québec méridional : 20 lacs de référence aux bassins versants non perturbés, 9 lacs ayant subi en 1995 des feux de forêt sur la majorité de leur bassin versant et 9 lacs ayant eu en 1995 une coupe à blanc sur une partie de leur bassin versant. Les communautés zooplanctoniques ont été caractérisées par différentes variables : 1) la composition, la richesse spécifique et la densité du zooplancton, 2) la masse organique du limnoplancton (seston > 53 µm) et 3) le biovolume du méso- et macrozooplancton (> 250 µm). La richesse spécifique et les assemblages d'espèces en juillet 1996 ne différaient pas entre les groupes de lacs ; la variation inter-réplicats dans les assemblages d'espèces de chaque lac était très faible en comparaison de la variation inter-lacs. Par contre, la densité du zooplancton et la masse organique du limnoplancton étaient en moyenne significativement plus élevées dans les lacs de feux que dans les lacs de coupes et les lacs de référence. Le biovolume du méso et macrozooplancton suivait les mêmes tendances. L'effet des traitements (groupes de lacs : référence, feu, coupe) expliquait moins de 15 % de la variance totale de la masse organique du limnoplancton et du biovolume du méso et macrozooplancton tandis que les différences inter-lacs expliquaient la majorité (> 70 %) de la variance totale dans ces indicateurs. Les 15 % de variance résiduelle étaient attribuables à la variation inter-réplicats dans chaque lac. Notre étude préliminaire indique que les feux de forêts provoquent une poussée trophique du zooplancton et du limnoplancton mais n'ont pas d'effet sur la biodiversité et les assemblages d'espèces de zooplancton. Par contre, les coupes de forêt n'accroissent pas la biomasse du zooplancton en dépit d'une légère augmentation des nutriments, car les apports plus importants en carbone organique dissous après la coupe limitent la production biologique. Les changements limnologiques d'un lac à l'autre ont beaucoup plus d'importance que les feux et les coupes de forêts dans le contrôle environnemental du zooplancton des lacs de la forêt boréale

Bridging the research-implementation gap in IUCN Red List assessments

The International Union for Conservation of Nature (IUCN) Red List of Threatened Species is central in biodiversity conservation, but insufficient resources hamper its long-term growth, updating, and consistency. Models or automated calculations can alleviate those challenges by providing standardised estimates required for assessments, or prioritising species for (re-)assessments. However, while numerous scientific papers have proposed such methods, few have been integrated into assessment practice, highlighting a critical research–implementation gap. We believe this gap can be bridged by fostering communication and collaboration between academic researchers and Red List practitioners, and by developing and maintaining user-friendly platforms to automate application of the methods. We propose that developing methods better encompassing Red List criteria, systems, and drivers is the next priority to support the Red List