Lars Kamp-Nielsen

Are seagrass growth and survival constrained by the reducing conditions of the sediment

A literature review of the effects of the reducing conditions of the sediment on seagrass metabolism, growth and survival, and of the morphological and physiological adaptations that seagrasses show to cope with sediment anoxia is presented and major gaps in knowledge are identified. The hypothesis that sediment anoxia controls the survival of seagrasses was tested experimentally by increasing the oxygen demand of the sediment with the addition of sucrose. Experiments were performed in a tropical (Southeast Asia) multispecific seagrass meadow, a Mediterranean Cymodocea nodosa meadow, and a temperate Zostera marina meadow. Sulfide levels in pore water and vertical redox profiles were used to characterise the effects of the sucrose additions on the sediment, while plant responses were quantified through the changes in shoot density and leaf growth. Sulfide levels in pore water increased and sediment redox potential decreased after the addition of sucrose to the sediment of different seagrass meadows. The effect of the addition of sucrose to the sediment of seagrasses was species-specific. Leaf growth was reduced and shoot mortality increased in some of the tropical species (e.g., Thalassia hemprichii), but not in others. Neither mortality nor leaf growth of the Mediterranean species C. nodosa was affected by sucrose additions, and only leaf growth was reduced two months after the addition of sucrose in Z. marina. Our results suggest that increased sediment anoxia might be a factor promoting growth inhibition and mortality in seagrasses, although strong differences have been found among different species and environments.

Phosphorus in Soil, Water and Sediment: An Overview

The geochemistry, availability and abundance of different forms of phosphorus in soil, water and sediments are reviewed. The present knowledge of phosphorus pathways in ecosystems and their regulation is discussed.In a drainage basin, anthropogenic phosphorus is brought into the system mainly as fertilizers and detergents. Sewer systems and outwash processes transfer the phosphorus from the terrestrial environment to the aquatic part of the ecosystem where an accumulation occurs in the sediments of the watercourse.A great part of the phosphates in soil is sorbed to soil particles or incorporated into soil organic matter. The release and export of phosphorus from uncultivated soil is a function of the geology and soil composition, but also of the air temperature, precipitation and the hydrological condition, pH etc.The solubility of phosphates is controlled by either sorption-desorption or precipitation-dissolution reactions depending on the environment in the soil or sediments. In soil and sediments with large amounts of iron and aluminium hydrous oxides, sorption-desorption reactions are largely responsible for determining the level of orthophosphate in the solution at equilibrium.Algal availability of phosphorus associated with soil-derived materials present in aquatic systems deserves more research. In addition, processes responsible for transport of phosphorus from cropland to aquatic systems and chemical and microbial transformations of phosphorus in lakes and streams deserve more attention.

Description of the three shallow estuaries: Mondego River (Portugal), Roskilde Fjord (Denmark) and the Lagoon of Venice (Italy)

The paper describes three European estuaries which were compared with respect to the dynamics between autotrophic components under the MUST-project: The Mondego River (M) (Portugal), Roskilde Fjord (R) (Denmark) and Venice Lagoon (V) (Italy). The areas of the three estuaries are (M) 3.4, (R) 125 and (V) 540 km2 and their maximum tidal ranges are (M) 3.3, (R) 0.2 and (V) 2.2 m. They are all eutrophic with high loadings of nitrogen (M) 126 t N/yr, (R) 2500 t N/yr and (V) 7000 t N/yr and high loadings of phosphorus (M) 1 t P/yr, (R) 180 t P/yr and (V) 1000 t P/yr. The dominating phytoplankton species are (M) diatoms and dinoflagellates, (R) Skeletonema sp. and (V) Amphora sp. and Chaetocerus sp. and the dominating macrophytes are (M) Enteromorpha sp., Gracilaria sp. and Zostera noltii, (R) Zostera marina and Ulva lactuca and (V) Ulva rigida and Zostera noltii. All three estuaries are frequently exposed to collapses caused by severe oxygen depletion.

Empirical and theoretical models of phosphorus loading, retention and concentration vs. lake trophic state

Models describing the dependence of lake trophic state on external phosphorus loading are of two general types: empirical, steady state models derived from statistical treatment of data from large numbers of lakes, and theoretical, dynamic models based on more or less detailed mathematical descriptions of kinetics of nutrient and population dynamics.In the former type of models, inlake P concentrations have been found to depend mainly on inflow P concentrations and on water residence time. Efforts to explain the remaining variance by other factors such as iron, calcium, alkalinity, etc. have generally not been successful. Relations between lake P concentrations and chlorophyll may be useful for the prediction of maximum chlorophyll levels with some confidence but large variations in the actual chlorophyll concentrations are caused by, e.g. zooplankton grazing, varying chlorophyll content of the algae and other limiting nutrients.Dynamic, theoretical models are more suited for the prediction of rates of response to perturbations than the empirical steady state models. Due to the much larger demand for input data and labour investment, these models are generally more suited for the scientist as tools for formalizing and testing hypotheses, than for the water manager. Simple models with flexible structure generally have advantages over complex models.Both empirical and theoretical models are potentially powerful tools in eutrophication research and management. It is important for both scientists and water managers to select the optimum complexity with regard to the problem to be solved and to the resources available in each case.

A kinetic approach to the aerobic sediment-water exchange of phosphorus in Lake Esrom

Abstract An empirical equation for the temperature-dependent sediment-water exchange of phosphorus, describing exchange as the sum of desorption, diffusion and biological degradation processes, is derived from previous experiments and observed temperature-exchange relationships. Additional equations for littoral and profundal exchange rates are developed. Calculated exchange values are compared with observed exchange values and the ratio: nitrogen released/phosphorus released compared with the sedimentation of phosphorus.

Validation of a prognosis based upon a eutrophication model

Abstract A prognosis, previously published together with the applied model in 1978, has been validated, and the results are presented in this paper together with a prognosis validation of an improved version. The characteristics features of the two model versions and the lake characteristics for the case study are given. The validation shows that acceptable model prognoses can be set up, but that flexible structure models probably would do a better job, as a shift in the species composition was observed, when the nutrient loading was reduced significantly.

Loss, growth and transport dynamics of Chaetomorpha aerea and Ulva rigida in the Lagoon of Venice during an early summer field campaign

The growth, the losses by grazing and sporulation and the advective transport of benthic macrophytes, dissolved and particulate nutrients were studied in the Lagoon of Venice during May–June 1995. The growth rate of Ulva rigida was 0.043 d−1 and the grazing rate found to be 0.01 d−1. No sporulation was observed in the study period. The advective transport of macrophytes was measured by catches in vertically exposed nets during several tidal excursions and varied from 0 to 11 kg Chaetomorpha aerea, 10 kg Zostera sp. and 9 kg Ulva sp. wwt. hour−1 per 2 m net length normalized to effective length perpendicular to the current direction. The transport of Chaetomorpha and Ulva was linearily correlated to the current velocity (r2 = 0.80 and 0.88 respectively). Vertically separated nets revealed that 89% of the Zostera sp. was transported in the top 30 cm of the water column and 65% of the Chaetomorpha sp. was transported in the deepest 30 cm of the column and the transport of Ulva sp. was dispersed over the 1 m water column. Automatically taken water samples were analysed for dissolved inorganic nutrients (carbon, nitrogen and phosphorus) and particulate nutrients during the campaign periods together with nutrients bound in macroalgae and seagrasses. The advective transport of dissolved and non-macrophyte bound, particulate nutrients were calculated by a 2-dimensional, hydrodynamic model. Less than 1% of the nutrients were transported as dissolved inorganic nitrogen and phosphate, 3–4% was transported as non-macrophyte, particulate nitrogen and phosphorus and more than 90% of the nutrients were transported as macrophyte bound nutrients. It is therefore obvious that mass balance calculations for shallow estuarine systems should include advective transport of dead and alive macrophytes.

Experimental evaluation of the effects of siltation-derived changes in sediment conditions on the Philippine seagrass Cymodocea rotundata

This study investigated if siltation-associated changes in the sediments are detrimental to seagrasses. We chose Cymodocea rotundata as the test species because it is considered one of the Southeast Asian seagrass species most sensitive to siltation. The approach included the (1) evaluation of the effects of silted sediments on plant growth, evaluation of the effects of in situ sulfide additions to the sediment on (2) the production of shoots, rhizomes and roots, and on the elongation rate of the horizontal rhizomes of plants located at the edge of a meadow, and on (3) leaf growth, mass allocation patterns and shoot density in a well-developed seagrass meadow. The results showed that under high light availability, major changes in sediment conditions associated with siltation did not negatively affect the plants but enhanced their growth likely by increasing the availability of nutrients. Pore water sulfide concentrations of 1 mM reduced by more than half the production of shoots, rhizome and roots, and the elongation rates of horizontal rhizomes of C. rotundata plants at the edge of the meadow, but had no effects on leaf growth and shoot density in a well-developed C. rotundata meadow.

Parameter estimation in eutrophication modelling

Abstract A procedure to estimate parameters for a eutrophication model using an intensive measuring program is described. The set of parameters do not perform a better validation, but it is possible to obtain a unique set of parameters, while the calibration method carried out on the basis of bi-monthly measurements gives several solutions to the parameters, all offering approximately the same validation. In addition, a few of the parameters estimated by the method presented here will get more realistic values. The sensitivity of the parameters estimated is such that it might, under changed loadings of nutrient, be of importance to use the unique set of parameters based on the intensive measurements rather than an occasional set of parameters among many possible solutions, which are obtained by normal calibration procedures. The paper also demonstrates how the method can be applied to select the best possible process description.

A submodel for anaerobic mud-water exchange of phosphate

Abstract A submodel for anaerobic mud-water exchange of phosphate is obtained from experiments in the laboratory. Phosphorus in the sediment can be divided into exchangeable and non-exchangeable phosphorus. The exchangeable phosphorus is decomposed in accordance with a first-order reaction. The phosphorus moves, after the decomposition process, from the interstitial water to the water phase, in accordance with a diffusion expression. The yearly increase of the sediment was determined by means of the lead concentration as a function of the depth.