Sediment Nutrient Enrichment Research Articles

Nutrient enrichment drives the sediment microbial communities in Chinese mitten crab Eriocheir sinensis culture

Microbial communities play a critical role in aquaculture ecosystems. To identify the influence of sediment nutrient levels on microbial communities, sediment and water samples were collected from Chinese mitten crab Eriocheir sinensis culture ponds with different nutrient enrichment levels. Relevant physicochemical properties were measured, and 16 S rRNA gene sequencing was applied to identify relevant bacterial communities in the sediments. The results showed that the diversity and composition of microbial communities in sediments with different levels of nutrient enrichment varied considerably. Proteobacteria was the most abundant phylum in all samples, followed by Bacteroidetes, and Desulfobacterota with relative abundances of 23.5–40.9%, 9.8–21.5%, and 9.6–18.1%, respectively. Notably, total nitrogen (TN), organic matter (OM), and pH were important factors driving sediment bacterial community aggregation, the TN concentration explaining 61.5% of the microbial community variation. This study highlights that long-term culture activities alter the degree of sediment nutrient enrichment, which in turn affects microbial community composition and may ultimately have an impact on culture efficiency.

Coastal Sediment Nutrient Enrichment Alters Seagrass Blue Carbon Sink Capacity.

The seagrass ecosystem is among the most efficient natural carbon sinks that can contribute to climate change mitigation. However, little is known about the effects of coastal nutrient enrichment caused by anthropogenic activities and/or climate change on the capacity of the seagrass blue carbon sink. Our experimental manipulations of sediment nutrient enrichment shifted the blue carbon sink capabilities of seagrass meadows. Sediment nutrient enrichment significantly increased the nutrient content of seagrass litter, stimulating the decomposition of rhizome + root litter by ∼10% while retarding the decomposition of leaf litter by ∼5%. Sediment N + P enrichment increased seagrass growth and litter production, while enrichment of N or P alone did not. Organic carbon (Corg) stocks in the surface sediments (0-5 cm) were 34% higher than those in the control with N + P enrichment due to high litter production and the low decomposition rate of nutrient-enriched leaf litter. However, Corg stocks in the subsurface sediments (5-20 cm) did not increase with sediment nutrient enrichment, which is likely due to accelerated decomposition of rhizome + root litter. Our findings suggest that nutrient loading in coastal sediments alters the blue carbon sink and storage capacities in seagrass meadows by changing the rates of carbon sequestration and decomposition.

Growth and reproductive responses of the seagrass Zostera marina to sediment nutrient enrichment

Abstract Nutrient loading into coastal sediments is increasing due to anthropogenic activity and climate change. We examined the effects of sediment nutrient enrichment on the growth and reproduction of Zostera marina by adding nitrogen (N) and phosphorus (P) fertilizers into sediments. Areal productivity and shoot density increased by ca. 60% in N and N + P enrichment plots and by ca. 20% in the P enrichment plots. Biomass and shoot height were also higher in the N and N + P enrichment plots than in the P enrichment and control plots. These results suggest that sediment N availability was more important than P availability in stimulating the vegetative growth of Z. marina . The density and morphology of reproductive shoots and seed production increased in only the N enrichment plots. The sediment N enrichment stimulated both the vegetative growth and sexual reproduction, improving the meadow resilience through both sexual and asexual mechanisms. The P enrichment slightly increased only the vegetative growth and might have limited influence on seagrass reproduction. According to these results, the alteration of the sediment nutrient regimes might shift the balance between the vegetative growth and sexual reproduction of Z. marina. These findings may have important implications for the management of seagrass meadows under fluctuations in sediment nutrients caused by anthropogenic activity and climate change.

Multiple stressors and disturbance effects on eelgrass and epifaunal macroinvertebrate assemblage structure

Multiple forms of environmental change and anthropogenic pressure co-occur in coastal marine ecosystems. These external forces affect ecosystem structure, functioning, and, eventually, services to humans. Studies that include more than 2 simultaneous stressors are still needed to understand potential interactions among multiple stressors. We evaluated single and interactive effects of density reduction of Zostera marina L. (a habitat-forming species), shading, and sediment nutrient enrichment on the response of Z. marina and its associated epifauna over 10 wk. Shading had the greatest effect on reducing the eelgrass relative leaf elongation rate (RLE), non-structural carbohydrate reserves, and eelgrass shoot density. A reduced eelgrass density sustained higher epifaunal densities and increased the eelgrass RLE. Sediment nutrient enrichment increased eelgrass shoot density but decreased epifaunal richness, diversity, and total abundance. Our disturbance and pair of stressors differed in their influence on diversity measures, but all affected assemblage structure. Most of the changes to the epifaunal assemblage and diversity likely occurred due to altered habitat availability and epiphytic algae load. We observed additive, antagonistic, and negatively synergistic interactions among our treatments, while most of the cumulative effects showed dominance by one stressor over another. Our results highlight the importance of field experiments that are based on multiple disturbances and stressors to determine their interaction type on communities.

Water Column Turbidity Not Sediment Nutrient Enrichment Moderates Microphytobenthic Primary Production

Soft sediment intertidal habitats are under intense anthropogenic pressure resulting from increased land derived sediment and nutrient delivery. Long term, this can cause high water column turbidity and nutrient enrichment of sediment porewaters, which has cascading effects on coastal ecosystem functionality. However, how these stressors may interact and influence benthic productivity over alternating periods of submergence and emergence is largely unknown. This study investigates the effects of sediment nutrient enrichment (at three levels for 20 months) on benthic primary production at six sites in four New Zealand estuaries that spanned a gradient in water column turbidity. While nutrient enrichment had no detectable effect on microphytobenthic primary production, water column turbidity had a significant influence, explaining up to 40% of variability during tidal submergence, followed by temperature and sediment characteristics. In addition, negative net primary production (NPP) estimates and therefore net heterotrophy for the most turbid estuaries during tidal submergence resulted in an increased reliance on production during emerged periods, where NPP was positive across all sites. This study highlights the prominent role of water column turbidity over nutrient enrichment in moderating microphytobenthic production, and the increasing importance of emerged periods to maintain the health and functioning of coastal habitats.

Implications of nutrient enrichment for the conservation and management of seagrass Zostera muelleri meadows

Abstract Nutrient overenrichment in aquatic environments, or eutrophication, is increasingly affecting seagrass habitats around the world, leading to the degradation of seagrass ecosystems and the loss of associated ecosystem services. The resistance of seagrass to nutrient enrichment is believed to be site specific, yet the direct correlations between environmental factors and the resistance of seagrass meadows has not yet been adequately resolved. The response of seagrass beds to long‐term multiple‐level sediment nutrient enrichment represents a current research gap. This study therefore assessed the in situ long‐term influence of four levels of sediment urea fertilizer addition on Zostera muelleri plants using a manipulative experimental design at three sites with diverse sediment characteristics. Specifically, this study investigated the response of porewater nutrient concentration, seagrass morphology indices, and seagrass plant tissue carbon and nitrogen contents under experimental nutrient stress levels. Over a 13‐month experiment, sediment nutrient addition substantially increased the ammonium concentrations in the sediment porewater, significantly decreased seagrass morphology indices, and caused a carbon and nitrogen imbalance in plant tissues. Ammonium toxicity was more pronounced in seagrass meadows growing on sandy substrates with lower relative above‐ground biomass, which showed low resistance to eutrophication at sediment ammonium concentrations of up to 1 × 104 μM. Plants growing in muddy sand substrates with higher relative above‐ground biomass were more resistant to nutrient impacts, however, with a delayed negative response observed in response to higher nutrient concentrations (up to 1 × 105 μM). Our findings suggest that seagrasses in low‐nutrient sandy environments show more rapid responses to eutrophication, although seagrasses in both sandy and muddy substrates exhibited declines in response to a long‐term elevation of sediment nutrient concentrations. While continuing to assess the relative susceptibility of seagrass habitats across differing environments to inform coastal management, conservation efforts should allocate resources accordingly and prioritize reducing nutrient overenrichment in sensitive seagrass meadows.

The combined effects of sediment accretion (burial) and nutrient enrichment on the growth and propagation of Phalaris arundinacea

Sediment accretion (burial) and nutrient enrichment occur concurrently in lacustrine wetlands, but the role of these two aspects of sedimentation on macrophyte performance has rarely been examined. Here, we investigated the concurrent effects of sediment accretion and nutrient enrichment on the growth and propagation of Phalaris arundinacea L. using a factorial sediment burial by nutrient addition experimental design. Regardless of burial depth, nutrient addition increased biomass accumulation, shoot mass ratio, the number of rhizomes, and the length of ramets and rhizomes. While burial had little effect on plant growth and propagation, it had an interactive effect with nutrient addition on belowground growth and ramet production. These results indicate that P. arundinacea is tolerant to burial, which allows it to grow in habitats with high sedimentation rates. However, the enhanced growth and propagation of P. arundinacea following sedimentation were primarily related to nutrient enrichment. This suggests that nutrient enrichment of sediments, which occurs in many lacustrine wetlands, increases the risk of invasion by P. arundinacea.

In situ soft sediment nutrient enrichment: A unified approach to eutrophication field experiments

Adding fertiliser to sediments is an established way of studying the effects of eutrophication but a lack of consistent methodology, reporting on enrichment levels, or guidance on application rates precludes rigorous synthesis and meta-analysis. We developed a simple enrichment technique then applied it to 28 sites across an intertidal sandflat. Fertiliser application rates of 150 and 600gNm−2 resulted in pore water ammonium concentrations respectively 1–110 and 4–580×ambient, with greater elevations observed in deeper (5–7cm) than surface (0–2cm) sediments. These enrichment levels were similar to eutrophic estuaries and were maintained for at least seven weeks. The high between-site variability could be partially explained by the sedimentary environment and macrofaunal community (42%), but only at the high application rate. We suggest future enrichment studies should be conducted in situ across large environmental gradients to incorporate real world complexity and increase generality of conclusions.

Morphological and Physiological Responses to Sediment Nutrients in the Submerged Macrophyte Myriophyllum spicatum

To improve the understanding of morphological and physiological changes of submerged macrophytes in response to different nutrient availabilities, Myriophyllum spicatum (a widely used lake restoration species due to its eutrophic tolerance in China) was planted in low-nutrient (TN 0.47 mg g−1, TP 0.10 mg g−1) and high-nutrient (TN 2.20 mg g−1, TP 1.91 mg g−1) sediments. The high-nutrient treatment reflected the eutrophication conditions in most lakes in the Middle and Lower Yangzi River Basin. Our results showed that the high nutrient level significantly increased the total biomass and affected shoot morphology traits; whereas the low sediment nutrient level significantly increased the root length of M. spicatum. The sediment nutrient enrichment significantly decreased the plant carbohydrate concentrations. Soluble sugar was positively correlated with the plant growth; however, carbohydrate concentrations in the auto-fragments only differed throughout its production period. It is noteworthy that most traits of M. spicatum respond rapidly between the treatments. These data demonstrate that M. spicatum can achieve a trade-off between its growth and storage by adjusting the pattern of biomass allocation in response to different sediment nutrients. Our study also implies that such flexible strategies would help M. spicatum adapt to the eutrophic environments.

Biomechanical response of two fast-growing tropical seagrass species subjected to in situ shading and sediment fertilization

Although seagrasses experience strong hydrodynamic forces, little is known about their biomechanical response in spite of the potential importance for their ecological success. We investigated how light reduction and sediment-nutrient enrichment affect biomechanical and morphological properties of two short-lived tropical seagrass species: Halophila ovalis and Halodule uninervis. A 50-day manipulative field experiment of shading and sediment-nutrient enrichment versus a natural population (control) showed that both shading and nutrient enrichment made the leaves of Halophila ovalis weaker (lower FTS) and more elastic (lower ET). As the absolute breakability of leaves (FMAX) was not affected by either of the treatments, this implies that these changes in strength and stiffness resulted from the increase in leaf dimensions under nutrient enrichment (i.e., longer, wider and thicker leaves) and shading conditions (i.e., thicker leaves). In contrast, the biomechanical properties of H. uninervis leaves were less responsive and only became more extensible under shading while their biomechanics did not change under sediment nutrient enrichment. This limited response of H. uninervis might be due to the lack of morphological response in this species since leaves only became longer under nutrient enrichment. When comparing both species across treatments under shading (after normalizing them with their controls), H. ovalis became significantly weaker compared to H. uninervis, and the latter became more extensible. Under nutrient enrichment, H. ovalis became significantly more elastic compared H. uninervis. Overall we found that (i) biomechanical properties can be affected by environmental conditions, (ii) the responses were species specific, and (iii) seagrass morphology (leaf thickness and width) affected by environmental conditions will influence seagrass biomechanical properties. Further experimental studies on seagrass biomechanics are needed as present understandings of the acclimation of these properties and the consequences for species functioning are only starting to emerge.

Reduced carbon sequestration in a Mediterranean seagrass (Posidonia oceanica) ecosystem impacted by fish farming

We studied the relationship between sediment nutrient enrichment and carbon sequestration, using the ratio of gross primary production to respiration (P/R), in a fish- farming impacted and an unaffected Mediterranean seagrass (Posidonia oceanica) ecosystem in the Aegean Sea, Greece. Carbon (C), nitrogen (N) and phosphorus (P) sedimentation, nutrient pools in sediment and dissolved nutrients in pore water were significantly and posi- tively intercorrelated, indicating close linkage between sedimentation and sediment nutrient pools in seagrass meadows. C, N and P sediment pools were significantly enhanced in the impacted meadow throughout the year, even during winter when fish farming activity was low. In the impacted sediment, the increase in C and N was higher than P, reflecting a faster remineralization and uptake of P than C and N. The ecosystem P/R ratio decreased exponen- tially with sediment nutrient enrichment. Threshold values are given for C, N and P sedimen- tation rates and sediment pools, and for N and P concentrations in pore waters, after which P/R ratio in the seagrass meadow decreases below 1, indicating a shift from autotrophy to heterotrophy with sediment nutrient enrichment. Such a regime shift indicates a loss of storage capacity of the seagrass ecosystem, jeopardizing the key role of P. oceanica as a carbon sink in the Mediterranean.

Effect of Sediment Nutrient Enrichment and Grazing on Turtle Grass Thalassia testudinum in Jobos Bay, Puerto Rico

We examined the effect of nutrients and grazers on Thalassia testudinum in Jobos Bay, Puerto Rico by fertilizing sediment and manipulating grazer abundances. Bottom-up effects were variable: Added nutrients did not increase seagrass aboveground biomass, but decreased belowground biomass—perhaps as a result of less biomass being allocated to belowground structures in response to greater nutrient supply in porewater. Experimental fencing of 1.5 × 1.5 m plots provided shelter that attracted large aggregations of fish, including seagrass herbivores. Seagrass biomass and shoot density decreased with increasing abundance of herbivorous fish, indicating a significant top-down effect. There were interactions between nutrient supply, provision of shelter, and grazing pressure. Fertilization enhanced seagrass %N; however, %N also increased in unfertilized plots that were fenced, most likely due to uptake of N excreted from the large numbers of fish associated with the fences. Only plots where shelter was provided and fertilizer was applied to sediments exhibited evidence of heavy grazing, reducing both seagrass cover and aboveground biomass. In the unfertilized fenced plots, signs of grazing were fewer despite large abundances of fish and enhanced nutritional quality of seagrass leaves. This suggests the possibility that high nutrient availability in sediments lowered concentrations of chemical defense compounds in the seagrass and that cues other than %N may have been involved in stimulating grazing. This study highlights the complexity of bottom-up and top-down interactions in seagrass systems and the important role of refuge availability in shaping the relative strengths of these controls.

Effects of ultraviolet-B radiation and nutrient enrichment on the productivity of benthic microalgae in shallow coastal lagoons of the North Central Gulf of Mexico

Benthic microalgae (BMA) play important roles in shallow coastal systems. Few studies have addressed the combined effects of ultraviolet-B radiation (UVB) and nutrient enrichment on the productivity of BMA. Here we use field and microcosms experiments to explore the single and combined effects of ambient and increased UVB and sediment nutrient enrichment on the productivity of BMA in two shallow coastal lagoons of the North Central Gulf of Mexico. We found few negative effects of ambient and increased UVB levels, even though increased UVB levels were higher than liberal predictions of anthropogenic increase for the studied area. In contrast, we found several positive effects of sediment fertilization, although all positive effects were restricted to one of the lagoons. These results point to strong protective responses of BMA to UVB in the lagoons studied. Such protective responses do not appear to be limited by ambient nutrient availability. This study indicates that sediment nutrient enrichment is a more important driver for BMA, and by default for the ecological functioning of the lagoons studied, than current and predicted UVB levels. These conclusions, however, may not apply to other coastal systems, where the interactive effects of fertilization and UVB on BMA deserve further investigation.

Effects of nutrient enrichment and shading on sediment primary production and metabolism in eutrophic estuaries

The impact of anthropogenic eutrophication on the productivity and metabolism of estuarine sediments has received relatively little attention. In this study, we investigated the separate and combined effects of decreased light availability and sediment nutrient enrichment, 2 of the most important impacts of anthropogenic eutrophication, on sediment primary production and metabolism in 2 eutrophic subestuaries of Weeks Bay (Alabama, USA), seasonally, over a year. We found a signif- icant effect of shading on both sediment primary production and metabolism, mostly due to decreased photosynthetic rates of benthic microalgae coupled with simultaneous increases in sediment respira- tion rates. The ratio of mean production in non-shaded plots to that in shaded plots was close to 1 and tended to occur at natural bottom light intensities 600 µmol photons m -2 s -1 ). Nutrient enrichment had little effect on sediment primary pro- duction and metabolism in the estuarine sites studied; however, in some instances nutrient enrichment influenced the negative effects of reduced light on sediment net production. The results demonstrate that the impact of light reduction on sediment primary production and metabolism in a turbid, nutrient-rich estuary is greater than that of additional sediment nutrient enrichment.

Effects of water depth and litter accumulation on morpho-ecological adaptations of Eleocharis sphacelata

The morpho-ecological adaptations of Eleocharis sphacelata in response to water depth and the sequential effects of resultant differences in deep water conditions on the long term population dynamics were investigated based on the observations carried out in three stable homogeneous populations in Goulburn and Ourimbah, New South Wales, Australia from August 2003 to May 2005. The deep water populations attained a higher harvestable shoot biomass and a lower rhizome biomass with increased growth in root structure thus significantly enhancing the nutrient uptake rates leading to a higher accumulation of shoot bound macronutrients. However, the accretion of excessive amounts of autogenous shoot litter coupled with slower decomposition rates under anaerobic conditions in the two deep water populations led to higher nutrient enrichment in sediments and overlying water column causing subsequent eutrophication with signs of growth inhibition including typical stress symptoms like stunted growth and chlorotic shoots. The shallow water population that intermittently experienced alternative inundation-drawdown pattern depicted an unaffected continuation of seasonal growth affirming that strict water regime management practices coupled with timely mowing or the removal of accumulating litter are necessary to ensure long-term survival of healthy E. sphacelata stands when it is used in applications where deep water conditions prevail.

An experimental test of the mechanism by which suspension feeding bivalves elevate seagrass productivity

A field experiment utilizing mussel mimics and sediment nutrient enrichment was con- ducted to examine the effect of the mussel Modilous americanus on meadows of the seagrass Tha- lassia testudinum. The experimental design tested the separate factors of increased habitat structure and increased nutrient enrichment resulting from the presence of the mussels. Nutrient enrichment had a significantly positive effect on sediment porewater nutrient concentrations and a significantly negative effect on leaf tissue C:N, C:P and N:P ratios. Increased habitat structure had a significantly positive effect on epiphytic grazer densities and a significantly negative effect on epiphytic biomass. In addition, calculated % light reduction by epiphytes was significantly reduced by structure and significantly increased by nutrient enrichment. This study showed that the direct effect of nutrient enrichment by mussel biodeposition produced the greatest positive response in productivity of T. testudinum in the seagrass meadows of St. Joseph Bay, Florida. In other systems experiencing eutrophication, however, it is possible that increased habitat complexity may have the greater effect on seagrass productivity.

The limited effect of in situ phosphorus and nitrogen additions to seagrass beds on carbonate and terrigenous sediments in South Sulawesi, Indonesia

Seagrass response to in situ sediment nutrient enrichment with slow-release fertilizers was studied (4 to 5 months after fertilization) in three tropical seagrass beds in South Sulawesi, Indonesia. Nitrogen-addition and P-addition had no significant effects on seagrass biomass, shoot density, and leaf production in mixed seagrass beds in a terrigenous sandy bay and a carbonate sedimentary reef flat environment, simultaneously fertilized in 1990. An additional experiment using a slightly adapted methodology (1991) at another carbonate site, characterized by a more homogeneously vegetated, and largely monospecific seagrass meadow of Thalassia hemprichii, again showed no significant response of seagrass growth, biomass, and shoot density to fertilization. C and N contents of plant tissue, however, had increased significantly ( p<0.05) to 12–25% above the controls in response to N-addition at this locality. The relatively high ambient porewater nutrient concentrations (about 10 μM PO 4, about 100 μM NH 4) and rather low C:N:P ratios (565:18:1) in seagrass tissue, indicate that nutrient supply meets seagrass demand and provide an explanation for the lack of response to the manipulations. The relatively high porewater phosphate concentrations in carbonate sediments are attributed to the relatively coarse particle-size distribution of these sediments in the study area, which limits their adsorption capacity and prevents P-limitation of seagrass growth, which is generally considered to be characteristic of tropical carbonate-rich environments.