Call for cooperation to contain damage by Chile's salmon farms
The proposed Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) (Nature 465, 525; 2010) should be part of a broader complementary system of scientific input. This would help to coordinate data that fall under the remit of multiple international environmental agencies and agreements. And it would minimize the risks of duplication in scientific review and reporting. A global consultation of scientists and others, coordinated by DesertNet International and the United Nations Institute for Water, Environment and Health (www.desertnet-international. org), has suggested that an equivalent intergovernmental science-policy panel for land and water issues is needed. Otherwise, important independent questions are likely to be absorbed by the scientific bodies that advise on climate change and biodiversity loss. Crucial matters may not receive the policy attention they deserve if solely addressed by the Intergovernmental Panel on Climate Change and the proposed IPBES. Examples are the impacts of trends in population growth and demographic bulges; food and energy insecurity; migration; and ‘land and water grabbing’ by wealthy foreign companies in developing nations. Lindsay C. Stringer School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK e-mail: l.stringer@leeds.ac.uk Call for cooperation to contain damage by Chile’s salmon farms
Responses of nitrogen and carbon deposition rates in Comau Fjord (42°S, southern Chile) to natural and anthropogenic impacts during the last century
Abstract Carbon isotopes and C/N ratios are frequently used to separate allochthonous and autochthonous organic matter input into marine shelf sediments. We test the applicability of this approach for the sediment record from Comau Fjord in southern Chile (42°S) with the aim to reconstruct carbon and nitrogen mass accumulation rates and to determine their allochthonous and autochthonous sources for the last century. Comparisons with isotopic and geochemical signatures of potential organic matter sources demonstrate that mixtures between terrigenous soil and peat on the one hand and marine planktonic organic matter on the other hand readily explain variations of organic carbon ( δ 13 C org ) and nitrogen ( δ 15 N) isotopes as well as in C/N and N/C ratios and explain differences in absolute values of these parameters along a transect of cores. Nitrogen mass accumulation rates, calculated from δ 15 N and C/N ratio, and carbon mass accumulation rates, calculated from δ 13 C org and N/C ratios of terrigenous organic matter, varied considerably less compared to those of autochthonous planktonic organic matter. Autochthonous carbon accumulation rates increased from between 1.2 and 5.2 g m −2  a −1 at the beginning of the last century to values between 21.5 and 29.9 g m −2  a −1 around the turn of the millennium. Even if the highest amount of diagenetic degradation is considered the mass accumulation rates increased by at least a factor of 2 within the last decades of the 20th century. The reasons for such a shift in primary productivity are discussed (1) in terms of recent climatic change in northwestern Patagonia possibly having lowered fluvial inflow into Comau Fjord and (2) in relation to anthropogenic eutrophication by rapidly expanding aquaculture. Given that allochthonous mass-accumulation rates remained fairly constant, we conclude that anthropogenic eutrophication caused by aquaculture is the more likely explanation for increased carbon and nitrogen accumulation rates in the last two decades in Comau Fjord. Moreover, a new proxy for marine productivity versus clastic terrigenous input (Br/Ti ratio) is suggested for the Chilean fjord environment.
Lake Muzahi, Rwanda: limnological features and phytoplankton production
Lake Muhazi, a small lake of Rwanda (East Africa) was studied from 1986 to 1990. A dramatic decrease of the catch of Oreochromis niloticus (350 T y−1 in the fifties vs 30 T y−1 in 1982) suggested a loss of productivity or overfishing. In the same period, other ecological changes occurred: the submerged macrophytes regressed and there was a decrease in Secchi depth (0.65 m in 1987 vs 1.5 m in the fifties). Compared to other lakes of the same area, the plankton production seemed low. The results of the present study characterize lake Muhazi as a shallow lake with a rather unstable diurnal stratification and with slight differences in mixing regime between its eastern, deepest part and its western, shallowest part. Secchi disk depth does not vary seasonally to a large extent. The water has a rather high mineral content (conductivity of about 500 µS cm−1 at 25 °C) and low concentrations of dissolved N and P, except in the hypolimnion, where NHinf4sup+-N can be high.Two species, Microcystis aeruginosa and Ceratium hirundinella, account for most of the phytoplankton biomass, which is about 50–80 mg chlorophyll a m−2 in the euphotic zone, usually with little seasonal variation. Daily gross production estimates amount to about 6 to 9.5 g O2 m−2 d−1 with a significant difference between the two parts of the lake. Data on C:N and C:P ratio in the phytoplankton suggest that some N deficiency might occur in the eastern part. Moreover, the Zm:Zc ratio could also lead to rather low net production rates (0.21–0.25 d−1 for a mixed layer of 4 m)In conclusion, the primary production of lake Muhazi is medium for African lakes and the hypothesis that decreased planktonic production could account for a reduced fish production should be discarded. Whereas the present yield of the fishery is only 20 kg ha−1 y−1, the yield estimated from primary production ranges between 46 and 64 kg ha−1 y−1. This could be reached through proper management. Finally, some hypotheses are given to explain the ecological changes which occurred in the lake.