<p>The continuous discharge of sewage with significant nutrient loads into coastal waters, is causing a dramatic deterioration of the environment due to eutrophication processes. Actually, some practices are being taken into account in aquaculture as the integration of seaweed in fish-farming to control the level of nutrients generated. In order to study the capability of macroalgae for removing nutrients, six species of the Mediterranean Coast of Southern Europe (Corallina elongata, Ulva olivascens, Halopteris scoparia, Cystoseira mediterranea, Laurencia pinnatifida and Enteromorpha sp.) were studied in laboratory experiments. The specimens were incubated in different external nutrient load conditions to determine the uptake rate of nitrate and phosphate, and the internal concentrations of these species were analysed to obtain the concentration factor for both nutrients. </p><p> </p><p>The results obtained show that these algae remove nutrients efficiently from the medium and the uptake rates follow saturation kinetics in normal conditions.</p><p>U.olivascens had the highest uptake rate for both nitrate and phosphate while C.elongata and H.scoparia had the highest concentration factor for nitrate and phosphate respectively. These results indicate that integration of these species in intensive fish-farming may play an increasingly important role as a nutrient-removal system, alleviating eutrophication problems due to fed aquaculture.</p>

The continuous discharge of sewage with significant nutrient loads into coastal waters, is causing a dramatic deterioration of the environment due to eutrophication processes. Actually, some practices are being taken into account in aquaculture as the integration of seaweed in fish-farming to control the level of nutrients generated. In order to study the capability of macroalgae for removing nutrients, six species of the Mediterranean Coast of Southern Europe (Corallina elongata, Ulva olivascens, Halopteris scoparia, Cystoseira mediterranea, Laurencia pinnatifida and Enteromorpha sp.) were studied in laboratory experiments. The specimens were incubated in different external nutrient load conditions to determine the uptake rate of nitrate and phosphate, and the internal concentrations of these species were analysed to obtain the concentration factor for both nutrients. The results obtained show that these algae remove nutrients efficiently from the medium and the uptake rates follow saturation kinetics in normal conditions. U.olivascens had the highest uptake rate for both nitrate and phosphate while C.elongata and H.scoparia had the highest concentration factor for nitrate and phosphate respectively. These results indicate that integration of these species in intensive fish-farming may play an increasingly important role as a nutrient-removal system, alleviating eutrophication problems due to fed aquaculture.

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Plants, as sessile organisms, have evolved many strategies to survive in a changing environment. Three key phenomena are considered in the present study: (1) morphological changes associated with C allocation to roots and shoots in favour of the most limiting resource; (2) differential C allocation to root pieces growing in relatively high nutrient patches and (3) physiological adjustment to the nutrient environment by up- or down regulating specific nutrient uptake rates. Plants exist as individuals within populations or communities. The aim of this study was to explore some of the dynamics, with respect to the above phenomena, that even-aged monocultures display. To this end, an individual-based modelling approach was developed (Chapter 2). A Moore neighbourhood cellular automation was designed so that each plant had nine roots (eight in its eight neighbouring cells and one in the central cell below the shoot). Roots could deplete N and P from neighbouring cells. A diffusion term was introduced to allow the movement of N and P between cells following a concentration gradient. To avoid edge effects, a 30 x 30 cell array was implemented with a toroidal configuration. As well as homogenous nutrient distribution, heterogeneity was introduced into the array at fine, medium or coarse grain. The total N available within the array (either high or low) remained constant but was distributed differently according to the grain of heterogeneity. The individual unit of the cellular automation was a single plant growth model (SPM) that incorporates the three phenomena listed above (Chapter 3). Plants (SPM) were randomly allocated to cells within the array from a Gaussian distribution of initial plant weights. Each plant could grow and interact with its eight immediate neighbours. The SPM growth followed an expo-logistic curve.

Maintaining a supply of potable water is a growing concern in the USA, particularly in many southern and western states. One method of sustaining water supply in these areas is the use of greywater for commercial and residential landscape irrigation. Greywater is derived from residential use such as showers, laundering and bathing, and accounts for approximately 65% of residential waste water. I investigated the effects of municipal tap water, harvested rain water, washing machine and bath water (greywater) on the carbon and nutrient dynamics of soil, foliage and leachate and on soil microbial diversity. I also examined the presence or absence of E. coli in source water and leachate. There was a significant difference in leachate chemistry among irrigation treatments. Average leachate pH and conductivity was significantly lower in treatments irrigated with harvested rain water. Fertilization did not affect any of the leachate chemistries with the exception of orthophosphate-P, but significantly reduced carbon in soil without grass (blank) and domestic tap water treatments. E. coli colonies were detected in source water (greywater), but not in leachate suggesting that there was no movement through the soil profile. The results of principal component analysis (PCA) on whole-soil fatty acid methyl ester (FAME) profiles indicated distinct differences in soil microbial community composition due to irrigation with greywater as compared to rainwater, suggesting that water source may affect soil microbial community composition.