Assessing the trophic state and eutrophication of coastal marine systems: a new approach based on the biochemical composition of sediment organic matter (original) (raw)
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Estuaries, 2003
In order to classify the trophic state of detritus sink systems, instead of the conventional indicators based on inorganic nutrient availability and algal biomass and productivity in the water column, we used new biochemical descriptors based on the amount of sedimentary organic carbon (C) and nitrogen (N) potentially available to hetero-trophs. We investigated spatial and temporal changes in microphytobenthic biomass, organic matter biochemical com-position, and enzymatically hydrolyzable protein and carbohydrate pools along a northsouth transect in the Marsala lagoon (Mediterranean Sea, Italy) at three stations characterized by different hydrodynamic conditions and organic matter content in the sediment. In the Marsala lagoon water currents decreased from north to south and this pattern was reflected by organic matter distribution and composition. Sediment organic matter concentrations were among the highest reported in the literature and, in the central area where large meadows of the seagrass Posidonia oceanica were present, display a strong dominance of highly refractory carbohydrates. The protein to carbohydrate ratio was always , 1, indi-cating the dominance of aged organic detritus. Microphytobenthic biomass displays an increasing pattern southward, and its contribution to the biopolymeric C pools ranged from negligible in the central sector of the lagoon to 50% in its northern part, indicating that sources of sediment organic C also changed along the hydrodynamic gradient. The per-centage contribution of the enzymatically hydrolyzable fraction of proteins and carbohydrates was inversely related to total protein and total carbohydrate concentrations, respectively, suggesting that bioavailability of organic C and N in-creased with decreasing organic matter content in the sediment and with increasing hydrodynamic regime. Microphyto-benthic contribution to biopolymeric C (as a proxy of autotrophic organic C) and the ratio of the enzymatically digestible fraction to biopolymeric C (as an indicator of organic matter liability) were significantly correlated, suggesting that chlorophyll a sediment content might be used as an indicator of food promptly available to consumers. The present study also highlighted that the ratio of labile (i.e., enzymatically digestible) versus biopolymeric organic C in the sediments tends to decrease with increasing organic matter content, due to the increase of the refractory fraction of organic C.
Marine Ecology Progress Series, 2007
We tested the effect of additions of organic matter of different quality (C:N ratio) and quantity on benthic fluxes of ammonium, nitrate, silicate, oxygen and dissolved inorganic carbon (DIC). Additions were made to intact sediment boxes, according to a 2-level factorial design, and the magnitude and temporal scale of the response were evaluated with Partial Least Square (PLS) regression analysis. Response patterns were followed over a 40 d period following the addition, but only fluxes of ammonium, nitrate, silicate and oxygen for the first 2 d after addition, and nitrate fluxes for the first 8 d after addition, could be used for predictive modelling. The results showed that the response of the microbial community to different qualities and quantities of organic matter may initially be related to its capacity to sequester organic matter, and in the long term, to its growth in response to the respective nutritional supply. The results also suggest that such an experimental approach can be a useful tool for classification of areas with potential risk of eutrophication.
Quantity and bioavailability of sediment organic matter as signatures of benthic trophic status
Marine Ecology Progress Series, 2009
Tools used for assessing marine trophic status are generally based on water column characteristics, which, however, may provide unreliable classification of the benthic trophic status. Here, we provide evidence from the literature that quantity and bioavailability of sediment organic matter are reliable proxies to assess benthic marine trophic status. We compiled data on the protein, carbohydrate and lipid concentration of sediments from different oceanic and coastal regions and varying water depths. The concentration of these 3 components as a whole (biopolymeric carbon) was found to be significantly correlated (r = 0.84) with the total organic carbon concentration, suggesting that the biopolymeric fraction is representative of the total organic carbon pool. However, the systematic variation of the biopolymeric fraction was higher than that of total organic carbon concentrations, suggesting that biopolymeric carbon is a more sensitive proxy of benthic trophic status than is the total carbon pool. Furthermore, biopolymeric carbon was significantly correlated to the amount of phytopigments, indicating that biopolymeric carbon accumulation in the sediment is related to inputs of algal carbon. Biopolymeric carbon concentrations were also positively correlated to the sediment community oxygen consumption, suggesting that the progressive accumulation of biopolymeric carbon could be an additional co-factor potentially responsible for hypoxic or anoxic events. The enzymatically digestible and algal fractions of biopolymeric carbon decreased in sediments with increasing biopolymeric carbon content (i.e. eutrophic systems), suggesting that organic carbon in eutrophic sediments is mostly refractory in nature. We propose that a biopolymeric carbon concentration in the sediment of > 2.5 mg C g-1 , being associated with a bioavailable fraction of <10%, can be considered as a threshold level at which benthic consumers may experience mostly refractory organic carbon.
Hydrobiologia, 2003
Ten beaches subjected to different wave action exposure were studied on the northwest coast of the Iberian Peninsula. According to descriptions of beach types (from very sheltered to very exposed) given by , five of the beaches studied were classified as sheltered and the other five as exposed beaches. The biochemical composition (proteins, lipids and carbohydrates) of sedimentary organic matter was analysed from the surface sediment down to a depth of 25 cm, between July and September 1997, at three tidal levels: high, medium, and low, at ebb tide. Biochemical compound concentrations were significantly higher in the sheltered than in the exposed beaches. Concentrations were, on average two, three and four times higher (for proteins, carbohydrates and lipids, respectively) in sheltered than in exposed sediments. The low hydrodynamic conditions of the sheltered beaches favoured the settlement of sedimentary organic matter. This is supported by the higher protein to carbohydrate ratio found in the exposed (12.3), in contrast with the sheltered localities (5.2). Sheltered but not exposed sediments were characterised by clear vertical profiles of protein, carbohydrate and lipid concentrations, with values on top approximately twice as high as in the deeper sediment layers. On the other hand, there were significant differences in the biochemical compound concentrations among tidal levels for both groups of intertidal localities, except for the protein concentrations in sheltered localities. Biochemical compound concentrations were higher at medium and low tidal levels for both sheltered and exposed beaches. In the three tidal levels, there was a significant negative relationship between the biopolymeric carbon and the intertidal slope. Thus, the biopolymeric carbon concentration decreased as the intertidal slope increased.
Organic carbon content of sediments as an indicator of stress in the marine benthos
Marine Ecology Progress Series, 2005
While organic matter in sediments is an important source of food for benthic fauna, an overabundance can cause reductions in species richness, abundance, and biomass due to oxygen depletion and buildup of toxic by-products (ammonia and sulphide) associated with the breakdown of these materials. Moreover, increasing organic content of sediment is often accompanied by other chemical stressors co-varying with sediment particle size. In the present study, synoptic data on the structure of macroinfaunal communities and total organic carbon (TOC) content of sediment were obtained from 951 stations representing 7 coastal regions of the world: the northern Black Sea (Crimean and Caucasian coasts); eastern Mediterranean Sea (Greece); North Sea (Ekofisk oil field); Firth of Clyde and Liverpool Bay, UK; Seto Inland Sea, Japan; Boston Harbor and Massachusetts Bay, USA and estuaries of the southeastern USA. Macroinfaunal and TOC data were examined to look for patterns of association consistent with conceptual model predictions and to identify TOC critical points corresponding to major shifts in the benthic data. Species richness, Hurlbert's E (S n ), was selected as the primary response parameter. Results suggested that risks of reduced species richness from organic loading and other associated stressors in sediments should be relatively low at TOC concentrations less than about 10 mg g -1 , high at concentrations greater than about 35 mg g -1 , and intermediate at concentrations in between. Predictive ability across these ranges was high based on results of re-sampling simulation. While not a measure of causality, it is anticipated that these TOC critical points may be used as a general screening-level indicator for evaluating the likelihood of reduced sediment quality and associated bioeffects over broad coastal areas receiving organic wastes and other pollutants from human activities.
Ecological Indicators, 2006
We applied a thermodynamic and network analysis on the micro and meio-benthic community in a wide coastal area of the southern Adriatic Sea in order to assess ecosystem health and to identify useful descriptors of environmental quality. The analysis of the micro and meio-benthic system in terms of organic matter, bacteria, microphytobenthos and meiofauna reflected changes occurring in the trophic state of benthic ecosystems and provided a tool for comparison between different environments. The biopolymeric carbon load never reached very high concentrations. Within these trophic conditions, ascendency, exergy and specific exergy resulted strictly related to each other and an increase of all the goal functions was observed at increasing resource availability. The analysis of trophic efficiency was particularly sensitive to assess the environmental state in term of sustaining complex structure and resource exploitation. In particular, specific exergy, ascendency/capacity and Finn's cycling index showed lowest values in more anthropogenic areas and can be proposed as candidate indices for the health assessment of coastal ecosystems. #