David P. Gillikin

Strong kinetic effects on Sr/Ca ratios in the calcitic bivalve Pecten maximus

Although Sr/Ca ratios in abiogenic calcite are strongly controlled by precipitation rates, such a kinetic effect has never been demonstrated in calcitic bivalve shells. Therefore, we report Sr/Ca ratios together with daily growth rates in the calcitic shells of four individuals of the bivalve Pecten maximus (age class I). Ratios of Sr/Ca were found to be variable among individuals that grew at the same location, illustrating that vital effects dominate over environmental controls. Although daily growth rate was correlated with shell Sr/Ca ratios, it explained only half of the Sr/Ca variations. However, daily shell surface area increment, an estimation of the total quantity of carbonate precipitated for a given time, explained 74% of the Sr/Ca variability in the shells of P. maximus. This proves, for the first time in a calcitic bivalve, that shell Sr/Ca partitioning is mainly controlled by kinetic effects. The Sr/Ca ratio should therefore be tested as a potential proxy of calcification rate in modern or fossil calcitic biocarbonates.

Modified AIC and MDL model selection criteria for short data records

The classical model selection rules such as Akaike information criterion (AIC) and minimum description length (MDL) have been derived assuming that the number of samples (measurements) is much larger than the number of estimated model parameters. For short data records AIC and MDL have the tendency to select too complex models. This paper proposes modified AIC and MDL rules with improved finite sample behavior. They are useful in those measurement applications where gathering a sample is very time consuming and/or expensive.

Use of stable isotopes to understand food webs and ecosystem functioning in estuaries

Stable isotopes have been extensively used to trace element cycles and their incorporation into food webs. This chapter provides a brief introduction to the principles of using stable isotopes as natural or deliberate tracers in estuarine systems, with a focus on (1) assessing the origin and cycling of organic and inorganic elements (mainly carbon and nitrogen), (2) defining estuarine food webs, (3) assessing animal movement or migration, and (4) interpreting stable isotope records in biogenic carbonates as proxies of (past) environmental conditions.

THE SUBURBAN STREAM SYNDROME: EVALUATING LAND USE AND STREAM IMPAIRMENTS IN THE SUBURBS

Development is known to impair stream water quality at moderate to high levels of urbanization, but the effects of low-density urban expansion, the kind occurring on the outskirts of many cities, remain unclear. We examined five suburban headwater streams in Duchess County, New York whose watersheds contained between 4.7% and 34% impervious surface cover. We measured Cl- and nitrate-N (NO3-N) concentrations in water samples taken at four to six sites on each stream in winter and summer. Even at low levels of population and impervious cover, concentrations of both Cl- and NO3-N exceeded reference levels found in cleaner streams in the region. Chloride levels were elevated in upper reaches and remained elevated or continued to increase downstream, with a linear response to impervious cover. Nitrate-N increased downstream in all watersheds, indicating that NO3-N inputs exceeded natural denitrification and uptake in both winter and summer. Nitrate-N responded logarithmically to impervious surface cover, with steep increases at low levels of imperviousness. Per-capita inputs were also high in rural areas. Agricultural inputs were not sufficient to explain observed trends in NO3-N; we interpret inputs to result chiefly from low-density exurban expansion. Widespread residential expansion has significant impacts on water quality that have not previously been acknowledged.

Contrasting biogeochemical characteristics of the Oubangui River and tributaries (Congo River basin)

The Oubangui is a major tributary of the Congo River. We describe the biogeochemistry of contrasting tributaries within its central catchment, with watershed vegetation ranging from wooded savannahs to humid rainforest. Compared to a 2-year monitoring record on the mainstem Oubangui, these tributaries show a wide range of biogeochemical signatures, from highly diluted blackwaters (low turbidity, pH, conductivity, and total alkalinity) in rainforests to those more typical for savannah systems. Spectral analyses of chromophoric dissolved organic matter showed wide temporal variations in the Oubangui compared to spatio-temporal variations in the tributaries, and confirm that different pools of dissolved organic carbon are mobilized during different hydrological stages. δ13C of dissolved inorganic carbon ranged between −28.1‰ and −5.8‰, and was strongly correlated to both partial pressure of CO2 and to the estimated contribution of carbonate weathering to total alkalinity, suggesting an important control of the weathering regime on CO2 fluxes. All tributaries were oversaturated in dissolved greenhouse gases (CH4, N2O, CO2), with highest levels in rivers draining rainforest. The high diversity observed underscores the importance of sampling that covers the variability in subcatchment characteristics, to improve our understanding of biogeochemical cycling in the Congo Basin.

INFLUENCE OF OPEN SPACE ON WATER QUALITY IN AN URBAN STREAM

Much attention has been given to the impairment of streams in urban areas and to the value of green space in preventing degradation. However, few studies have examined whether green space can remediate water quality downstream of contaminant sources. To assess the degree to which an ecological preserve was able to ameliorate upstream water quality impairments, we examined changes in conductivity, total inorganic nitrogen (TIN), and a family biotic index (FBI) for benthic macroinvertebrates in a partially urbanized stream in eastern New York state, USA. We expected conductivity, which results mainly from road de-icing salt, to decrease in the green space due to dilution from low-conductivity surface runoff. We also expected TIN and FBI to indicate stream improvements in response to increased vegetative cover in the green space. Contrary to expectations, conductivity did not improve in the ecological preserve, although TIN and FBI values did improve. Differences in scales of response explain this contrast in recovery/conductivity responded to basin-wide percentage impervious surface cover (ISC), while TIN and FBI responded to riparian-scale ISC, which declined sharply in the ecological preserve. Conserving riparian green space can aid natural recovery of TIN and FBI. In contrast, controlling conductivity requires watershed-wide management.

THE OCCURRENCE OF THE SEMI-TERRESTRIAL SHRIMP MERGUIA OLIGODON (DE MAN, 1888) IN NEOSARMATIUM SMITHI H. MILNE EDWARDS, 1853 BURROWS IN KENYAN MANGROVES

DAVID PAUL GILLIKIN1/, SAMMY DE GRAVE2/ and JURGEN F. TACK3/ 1/Laboratory of Ecology and Systematics, Mangrove Management Group, Free University Brussels, Pleinlaan 2, B-1050 Brussels, Belgium 2/Oxford University Museum of Natural History, Parks Road, Oxford OX1 3PW, United Kingdom 3/Belgian National Science Foundation, c/o Laboratory of Ecology and Systematics, Mangrove Management Group, Free University Brussels, Pleinlaan 2, B-1050 Brussels, Belgium

Do freshwater mussel shells record road-salt pollution?

Road-salt pollution in streams in the Northeastern United States has become a major concern, but historical data are scarce. Freshwater bivalve shells have the ability to record past environmental information, and may act as archives of road-salt pollution. We sampled Elliptio complanata shells from four streams, as well as specimens collected in 1877. Average [Na/Ca]shell was highest in modern shells from the stream with the highest sodium concentrations, and low in shells collected from this same stream in 1877 as well as in the shells from other streams, suggesting that [Na/Ca]shell serves as a proxy for road-salt pollution. We expected higher [Na/Ca]shell in winter and spring. However, high-resolution [Na/Ca]shell analyses along the growth axis of one shell did not reveal any clear subannual patterns, which could be the result of shell growth cessation in winter and/or during periods of high stream sodium concentrations. Therefore, bulk [Na/Ca]shell analysis from multiple shells can be used as a proxy of large changes in stream sodium concentrations, but high-resolution variations in stream sodium concentrations do not seem to be recorded in the shells.

Seabirds supply nitrogen to reef-building corals on remote Pacific islets

Seabirds concentrate nutrients from large marine areas on their nesting islands playing an important ecological role in nutrient transfer between marine and terrestrial ecosystems. Here we investigate the role of guano on corals reefs across scales by analyzing the stable nitrogen isotopic (δ15N) values of the scleractinian coral Pocillopora damicornis on fringing reefs around two Pacific remote islets with large seabird colonies. Marine stations closest to the seabird colonies had higher nitrate + nitrite concentrations compared to more distant stations. Coral and zooxanthellae δ15N values were also higher at these sites, suggesting that guano-derived nitrogen is assimilated into corals and contributes to their nitrogen requirements. The spatial extent of guano influence was however restricted to a local scale. Our results demonstrate that seabird-derived nutrients not only spread across the terrestrial ecosystem, but also affect components of the adjacent marine ecosystem. Further studies are now needed to assess if this nutrient input has a positive or negative effect for corals. Such studies on remote islets also open fresh perspectives to understand how nutrients affect coral reefs isolated from other anthropogenic stressors.

OSMOREGULATORY ABILITY OF CHIROMANTES ORTMANNI (CROSNIER, 1965) SUBJECTED TO DILUTE AND HYPERSALINE SEAWATER

The short-term osmoregulatory ability and salinity tolerance of Chiromantes ortmanni was studied in the laboratory. C. ortmanniis a non-burrowing, high shore mangrove crab often subjected to extreme salinity e uctuations. They were found to be exceptional osmoregulators in salinities ranging from0 ‰ to65‰ after threedays. They could also osmoregulate in 80 ‰ for at least 24 hours, but 96‰ proved to be lethal after just 12 hours. Osmotic capacity suggests that they are best suited for salinities ranging from about 16 ‰ to 48‰. As they are frequently found in salinities higher than this, it is hypothesized that they tolerate the higher energetic costs of large osmotic gradients as a trade-off for other benee ts such as reduced predation and food competition.