Sediment Nutrient Availability Research Articles

Strong Saharan Dust Deposition Events Alter Microbial Diversity and Composition in Sediments of High-Mountain Lakes of Sierra Nevada (Spain)

Mediterranean high-mountain lakes are being increasingly affected by strong Saharan dust deposition events. However, the ecological impacts of these severe atmospheric episodes remain largely unknown. We examined the effects of a strong Saharan dust intrusion to the Iberian Peninsula in 2022 on the physicochemical parameters and prokaryotic communities in sediments of nine high-mountain lakes of Sierra Nevada (Spain) located above 2800 m.a.s.l and in different orientations (north vs. south). A previous year (2021), with lower Saharan dust deposition with respect to 2022, was used for interannual comparisons. The strong dust deposition to the high-mountain lakes resulted in a significant increase in sediment nutrient availability which was linked to changes in the composition of prokaryotic communities. Decreases in alpha diversity and changes in beta diversity of prokaryotic communities were mainly observed in lakes located in the south compared to the north orientation likely because the former was more affected by the atmospheric dust deposition episode. Dust intrusion to the high-mountain lakes resulted in significant changes in the relative abundance of specific genera involved in important nutrient cycling processes such as phosphate solubilization, nitrogen fixation, nitrification, and denitrification. Saharan dust deposition also increased predicted microbial functionality in all lakes. Our findings show that severe atmospheric dust inputs to remote high-mountain lakes of Sierra Nevada can have significant biogeochemical and biodiversity consequences through changes in nutrient availability and prokaryotic communities in sediments of these freshwater ecosystems. This information contributes to understanding how Mediterranean high-mountain lakes of Sierra Nevada face strong intrusions of Saharan dust and their ecological consequences.

The Effects of Long-Term Nitrogen Enrichment on Estuarine Benthic-Pelagic Coupling

Biogeochemical cycling in the marine coastal zone regulates the availability of nitrogen and carbon within soft sediment habitats. However, these pathways are being fundamentally altered by anthropogenic increases in nutrient delivery. Few studies have incorporated long-term enrichment and ecological complexity (in situ experiments), restricting our ability to manage effectively and prevent ecological shifts. This study investigates the influence of sediment nutrient availability (at 3 levels, across 2 seasons) on biogeochemical cycling over a 20-month period in 4 estuaries. Overall, net denitrification rates were highly variable, ranging between 4 and 208 µmol N m−2 h−1. However, no increases were observed with increasing enrichment highlighting the limited capacity for nitrogen removal in response to large increases in bioavailable nitrogen. Additionally, macrofaunal communities and sediment trophic status were shown to have important influences on nitrogen processing. Overall, alterations to ecosystem relationships and the appearance of non-linear responses to increasing nutrient enrichment reveal the vulnerability of estuaries to increasing stressor loads owing to the increased likelihood of reaching a tipping point.

Effects of debris piles and pools along dry riverbeds on nutrients, microbial activity, and ground-dwelling arthropods: A Namibian ephemeral river case

Debris piles and dry pools are common landscape elements along ephemeral river channels. However, their effects on resource availability and arthropod species diversity have been neglected so far. We investigated whether debris piles and pools along dry riverbeds generate nodes of environmental resources, influence microbial activity, and provide key habitats for ground-dwelling arthropods. We studied three different habitats (channel, debris pile and dry pool) to analyze organic matter, nutrients and microbial activity in dry sediments, and included two further habitats (riparian and upland areas) for ground-dwelling arthropod assemblages along a major ephemeral river (Ugab River, NW Namibia). We observed higher concentrations of organic matter and macro- and micro-nutrients in debris piles than in pools, and higher concentrations in both landscape elements than in the sandy channel matrix. Microbial activity showed a positive relationship with organic matter and nutrient availability in sediments. Debris piles, dry pools and channels harbored diverse and abundant ground-dwelling arthropod assemblages similar to adjacent terrestrial areas. Debris piles and pools differed in assemblage composition not only from riparian and upland areas but also from the sandy channel matrix. Overall, debris piles and dry pools acted as nodes of soil fertility, enhanced microbial activity, and shaped ground-dwelling arthropod assemblages.

Mass development of monospecific submerged macrophyte vegetation after the restoration of shallow lakes: Roles of light, sediment nutrient levels, and propagule density

After restoration, eutrophicated shallow freshwaters may show mass development of only one or two submerged macrophyte species, lowering biodiversity and hampering recreation. It is unclear which environmental factors govern this high percentage of the volume inhabited (PVI22PVI: The percent of the water volume inhabited by submerged macrophytes.) by submerged macrophytes, and whether the development of a more diverse, low canopy vegetation is likely to occur if dominant species decline in abundance.We hypothesized that (1) adequate light and high sediment nutrient availability leads to massive development of submerged macrophytes, and (2) that macrophyte species richness is low at high PVI, but that this is not caused by a lack of viable propagules of non-dominant species (especially charophytes).To test these hypotheses, fifteen shallow waters in the Netherlands were studied with respect to submerged vegetation (including propagules), water, and sediment characteristics.The probability of high submerged macrophyte PVI is highest in shallow waters where light availability in the water layer and phosphorus availability in the sediment are abundant. These conditions typically occur upon restoration of eutrophic waterbodies by reducing water nutrient loading or applying biomanipulation. Other factors, as top-down control, can additionally influence realised PVI. Viable propagules of species other than the dominant ones, including charophytes, were found in most of the sediments, indicating that once the dominant species declines, there is local potential for a diverse submerged vegetation to develop. Results can be used to predict when mass development occurs and to tackle the factors causing mass development.

Flooding tolerance and horizontal expansion of wetland plants: Facilitation by floating mats?

Water level fluctuations (WLF) can be important disturbances promoting the diversity of riparian plant communities, but are currently absent from many managed aquatic ecosystems. A lack of WLF is thought to reduce plant diversity and hamper hydrosere succession. However, a positive impact of WLF on plant diversity may crucially depend on nutrient availability and the presence of a potential ecosystem engineer, the floating plant Stratiotes aloides, that may provide structural support to riparian plants. We tested the interactive effects of 40cm flooding, presence of S. aloides and sediment nutrient availability (N and P) on growth and horizontal expansion of eight wetland plant species in a 10 week experiment. Seven out of eight species showed a significant elongation response to flooding. Compared to stagnant water levels, flooding in combination with high nutrient availability decreased horizontal expansion in two short species and increased it in two tall species, whereas flooding decreased horizontal expansion in two other short species under both nutrient levels. In this 10 week experiment, we observed no effect of S. aloides on the measured plant parameters. This experiment shows short-term negative effects of flooding on most of the short species. On the long-term, we hypothesize that improvements in water quality and seedling recruitment due to drawdown may result in net positive effects of WLF in the riparian zone, but as the species that were rare in the field happened to be short, care should be taken to maintain rare species when allowing more WLF.

Effects of Shoreline Development on Composition and Physical Structure of Plants in a South Carolina High Marsh

Increased freshwater and nutrient runoff associated with coastal development is implicated in dramatically altering estuarine communities along eastern US shorelines. We examined effects of three categories of shoreline development on high-marsh environments within Murrells Inlet, South Carolina, USA by measuring sediment nutrients, porewater salinity, plant species diversity, and above- and belowground plant biomass. Effects on new plant growth also were examined in plot clearing and transplantation experiments. Greater nutrient availability in sediments along developed shorelines was reflected in greater aboveground biomass and nitrogen storage in Juncus roemerianus plant tissue. Plant species composition was not significantly different among levels of shoreline development. Zinc concentrations were greater in sediments from developed shorelines and may represent an easily measured indicator of shoreline development. Recently accelerating shoreline development in the southeastern USA may alter plant production, nitrogen storage, and sediment metal content in salt marshes.

Long‐term nitrogen and phosphorus fertilization effects on N2 fixation rates and nifH gene community patterns in mangrove sediments

AbstractThe bioavailability of nutrients is important in controlling ecological processes and nitrogen cycling in oligotrophic mangrove forests, yet the variation of diazotrophic community structure and activity with nutrient availability in sediments remains largely unexplored. To investigate for the first time how nutrients in sediments affect spatial and temporal patterns of diazotrophic community structure and activity, the sedimentary environment of Twin Cays, Belize, was examined with respect to the effects of long‐term fertilization [treatments: control (Ctrl), nitrogen (N), and phosphorus (P)] on N2 fixation rates and nifH gene community structure. We found that N2 fixation rates were significantly higher at the P‐treatment, intermediate at the Ctrl‐treatment and lower in the N‐treatment (P: 4.2 ± 0.5, Crtl: 0.8 ± 0.1, N: 0.4 ± 0.1 nmol·N·g−1·h−1; P < 0.001) with spatial (Ctrl‐ and P‐treatments) and temporal (only P‐treatment) variability positively correlated with live root abundance (r2 = 0.473, P < 0.001) and concentration (r2 = 0.458, P < 0.0001). The community structure of diazotrophs showed larger spatial and temporal variability in the fertilized treatments than in the Ctrl‐treatment, with the relative abundance of OTUs (nifH operational taxonomic units) at the fertilized treatments inversely related to live root abundance. Overall, long‐term fertilization (with either N or P) affects not only nutrient levels in mangrove sediments directly, but also spatial and temporal patterns of both community structure and activity and likely plant‐microbe interactions as well. Our findings suggest that the maintenance of natural nutrient conditions in mangrove sediments is important to ensure the stability of microbial functional groups like diazotrophs.

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.

Growth, biomass allocation, and autofragmentation responses to root and shoot competition in Myriophyllum spicatum as a function of sediment nutrient supply

Plant growth, biomass allocation and autofragmentation were investigated in response to root and shoot competition in the submersed macrophyte Myriophyllum spicatum L. growing in two sediment environments. Biomass accumulation and allocation were significantly affected by sediment fertility, with a higher total biomass observed in fertile sediment (average: 4.69 g per plant vs. 1.12 g per plant in infertile sediment). Root-to-shoot ratios were 0.34 and 0.06 in the infertile and fertile sediments, respectively, reflecting the high investment placed on roots under infertile conditions. In the presence of root, shoot, and full competition, whole plant biomass decreased by 18%, 12% and 24% in the infertile sediments, and 23%, 25% and 33% in the fertile sediments, respectively. Root weight ratios (RWRs) increased with root competition by 38% ( P < 0.001) and 12% ( P = 0.002), while leaf weight ratios (LWRs) decreased with shoot competition by 6% ( P = 0.042) and 5% ( P = 0.001) in the infertile and fertile sediments, respectively. A total of 406 autofragments were harvested in the fertile sediments, but none were obtained from the infertile sediments. In the control, autofragment number and biomass was 166% and 175% higher compared to the competition treatment. Root and shoot competition resulted in a 21% ( P = 0.043) and 18% ( P = 0.098) decrease in the autofragment biomass, respectively. These results indicated that M. spicatum responds to different sediment fertility by changing its allocation patterns. Moreover, both root and shoot competition influenced plant growth and autofragmentation, while sediment nutrient availability played an important role in M. spicatum autofragmentation.

Effect of an Alien Species Spartina alterniflora Loisel on Biogeochemical Processes of Intertidal Ecosystem in the Jiangsu Coastal Region, China

Spartina alterniflora Loisel, a species vegetating in intertidal flats along the eastern coast of the United States, was introduced in China almost 30 years ago and has become an urgent topic due to its invasiveness in the coastal zone of China. The impacts of this alien species S. alterniflora on intertidal ecosystem processes in the Jiangsu coastland were investigated by comparing the sediment nutrient availability and trace element concentration characteristics in a mudflat and those of a four-year old Spartina salt marsh that had earlier been a mudflat. At each study site, fifteen plots were sampled in different seasons to determine the sediment characteristics along the tidal flats. The results suggested that Spartina salt marsh sediments had significantly higher total N, available P, and water content, but lower pH and bulk density than mudflat sediments. Sediment salinity, water content, total N, organic C, and available P decreased along a seaward gradient in the Spartina salt marsh and increased with vegetation biomass. Furthermore, the concentrations of trace elements and some metal elements in the sediment were higher under Spartina although these increases were not significant. Also, in the Spartina marsh, some heavy metals were concentrated in the surface layer of the sediment. The Spartina salt marsh in this study was only four years old; therefore, it is suggested that further study of this alien species on a longer time frame in the Jiangsu coastland should be carried out.

Resource allocation in the submerged plant Vallisneria natans related to sediment type, rather than water‐column nutrients

Summary1. Phenotypic plasticity in resource allocation by Vallisneria natans was investigated in a greenhouse experiment, using three types of sediment [sandy loam, clay, and a 50 : 50 (by volume) mixture of the two sediments] and two levels of water‐column nutrient. The clay was collected from a highly eutrophic lake in Jiangsu Province, China, and the N and P concentrations applied in nutrient media were at the upper limits observed in most lakes of China.2. Growth and biomass allocation were significantly affected by sediment type, rather than water‐column nutrients. Plant growth in clay and the mixture were similar, and 2.4–3.4 times higher than that in sandy loam. Compared with the plants grown in clay or the mixed sediments, the plants grown in sandy loam allocated relatively more biomass to root (11–17% versus 7–8% of total biomass), and relatively less to leaf (76–82% versus 86–87% of total biomass). Plastic variations in root area were induced by sediment type alone (P &lt; 0.05), whereas the impacts of sediment type and water‐column nutrients on leaf area were insignificant (P &gt; 0.05).3. Plant N and P concentrations were significantly affected by both sediment type and water‐column nutrients. Increased nutrient availability in the water column enhanced plant N concentration by 3.5–20.2%, and plant P concentration by 19.1–25.8%.4. Biomass accumulation and plant nutrient concentration in plants grown in different sediment types and water‐column nutrients indicate that sediment type had more significant impacts on growth and N and P concentrations of V. natans than did water‐column nutrients. Changes in phenotype are a functional response to nutrient availability in sediment, rather than to water‐column nutrients.

Short-time response in root morphology of Vallisneria natans to sediment type and water-column nutrient

Rooted submerged macrophytes can absorb significant amounts of nutrients from both sediment and water. We investigated root morphology of Vallisneria natans in mesocosm plastic bins, in response to three types of sediment (sandy loam, clay, and a 50:50 (v/v) mixture of the two sediments) and two levels of water-column nutrient (well water and nutrient medium). Compared to the plants grown in the clay or mixed sediments, root diameter decreased (0.39–0.41 versus 0.36–0.37 mm) but total root length per plant increased (0.87–1.27 versus 1.14–1.62 m) when grown in sandy loam. Increase of nutrient availability in water column led to decreased specific root length (306–339 versus 258–281 m g −1). However, both sediment type and water-column nutrient had no impacts on root number (ranged from 19 to 24 number of roots per plant). Root weight ratio, root:leaf mass ratio and root:leaf length ratio generally decreased with enhanced nutrient availability in sediment or water. Plant growth was affected by sediment type alone ( P < 0.05), rather than water-column nutrient ( P > 0.05). However, plant N and P contents were significantly impacted by both sediment type ( P ≤ 0.001) and water-column nutrient ( P < 0.05). Increase of nutrient availability in sediment or water led to increased plant N (ranged from 2.47 to 4.77 mg g −1) and P concentrations (ranged from 42.8 to 62.0 mg g −1). These results indicate that considerable variation in root morphology of V. natans exists in response to the fertility of the sediment it is rooted in.

Spatio-temporal dynamics and plasticity of clonal architecture in Potamogeton perfoliatus

Above- and below-ground clonal growth architecture was compared for two neighbouring patches of Potamogeton perfoliatus L. in Lake Constance, representing typical sparse and dense growth types. A detailed map of individual ramets and their corresponding rhizome network was produced and the seasonal development of ramet sprouting and rhizome growth was reconstructed. Rhizomes extended at rates ranging between 40 and 63 cm per year, and added a new shoot for every 1–20 cm of rhizome produced. The main rhizome axis grew in a semi-linear fashion, with deviation means of 15 and 24°, and developed 0–0.5 branches per plant, with an insertion angle from 15–90°. Total rhizome length of all plants amounted to 5 and 11 m m −2 at the two sites. The total biomass produced at the two sites differed by 10-fold. The neighboring patches also showed different allocation patterns which are interpreted as foraging. Contrary to the prediction of the foraging hypothesis, there was only a small difference in mean spacer length between sites. On the other hand, the spacer length was plastic relatively to total biomass. We propose that spacer length is not an independent part of the foraging strategy, but rather a result of overall productivity and biomass allocation. Phosphorus content of plant tissue at the more productive site was two-fold higher than that at the less productive site which suggests that the different growth types may be due to differences in sediment nutrient availability: in situ fertilization of a less productive site increased the P content to those levels of the productive site. In situ fertilization also resulted in higher ramification, lower root allocation and decreased spacer length and confirmed the foraging capability of P. perfoliatus.

The effect of nutrient additions on bacterial activity in seagrass ( Posidonia oceanica) sediments

The influence of nutrient additions on benthic bacterial activity under seagrass meadows was tested by enriching five seagrass ( Posidonia oceanica) meadows with nutrients over one year. We found a highly significant response of benthic bacterial activity to nutrient additions, which was reflected in greater (about two-fold) ammonification rates and, to a smaller extent, a significant tendency for a greater exoenzymatic activity. Nutrient additions significantly raised bacterial activity, without altering the seasonal changes in bacterial activity. As a result of the increased bacterial activity, the organic content of the sediments declined significantly, by about 33%, after one year of nutrient addition. Hence, nutrient additions to the seagrass meadows enhance seagrass production but also accelerate bacterial decomposition of seagrass carbon, thereby reducing the capacity of the sediments to store organic carbon. These results demonstrate that sediment nutrient availability limits bacterial activity in these Posidonia oceanica meadows, and identify bacteria as important nutrient consumers in these systems.

Sediment interactions with submersed macrophyte growth and community dynamics

We review and synthesize information available in the literature on sediment interactions with submersed macrophyte growth and community dynamics. Sources of particular nutrients for uptake by submersed macrophytes are critically evaluated. Sediment physical and chemical properties are considered as a product of macrophyte growth as well as potential delimiters of growth. Aspects of macrophyte nutrition that influence littoral nutrient dynamics and macrophyte community composition are highlighted, with attention to factors affecting sediment nutrient availability. Interactive effects of sediment nutrient depletion, sedimentation, bioturbation, and microbial activity on macrophyte growth are emphasized. Major linkages and feedbacks between aquatic macrophytes and sediment properties are considered in terms of elemental exchanges and responses at the ecosystem level. Changes in macrophyte community composition during lake aging, or over relatively shorter time periods, are suggested to occur partially in response to altered sediment properties.

Interrelationships between the growth of Hydrilla verticillata (L.f.) Royle and sediment nutrient availability

On sediment planted with Hydrilla verticillata (L.f.) Royle compared with control (unplanted) sediment we measured >90% and >30% reductions in concentrations of exchangeable N and extractable P following two consecutive 6-week periods of growth. Diminished N availability, owing to prior plant uptake, resulted in a 30% reduction in Hydrilla growth. Concomitant increases (>30%) in the concentration of exchangeable K suggest that this element, obtained via foliar uptake from overlying water, may be exchanged by roots of Hydrilla for ammonium in sediment. We postulate that under N-limiting conditions, K translocation in this species from shoots to roots potentially increases the availability of sediment N. An important implication of these findings is that under some circumstances the growth of Hydrilla may be self-limiting.