Macrophyte Vegetation Research Articles

THE MACROPHYTE FLORA AND VEGETATION OF THE PAUČKO LAKE (MT. KONJUH)

UDK: 581.9:574.5 (497.6) (285)
 The study presents the first data on biodiversity of macrophyte flora and vegetation of Paučko Lake, which is recognized as an area of great natural, landscape and hydrological value in the Protected Landscape “Konjuh”. Paučko Lake has a small surface and it’s located at 711 m a.s.l. in the catchment area of the Drinjača River. The aquatic and marsh vegetation were studied during spring and summer in 2018 using the traditional Zürich-Montpellier approach. The vegetation of Paučko Lake is comprised of aquatic and marsh associations of the classes Potamogetonetea Klika in Klika et Novák 1941 and Phragmito-Magnocaricetea Klika in Klika et Novák 1941. The following aquatic and marsh plant associations were identified: Myriophyllo-Potametum Soó 1934, Scirpo-Phragmitetum australis W. Koch 1926, Thelypterido palustris-Phragmitetum australis Kuiperex van Donselaar et al. 1961, Schoenoplectetum lacustris Chouard 1924, Typhetum latipholiae Lang. 1973 and Scirpetum silvatici Ht et H-ić prov. (in Ht et al.1974). Rare vulnerable taxa Thelypteris palustris Schott and Menyanthes trifoliata L. were recorded in emerged littoral communities, whose habitats are under successional changes caused by excessive macrophyte overgrowth by competitor species. Restoration measures are necessary to be taken to preserve the habitats of endangered species of the Paučko Lake.

Metabolic Potential of Some Functional Groups of Bacteria in Aquatic Urban Systems

This study analyzed the metabolic potential of some functional groups of bacteria in aquatic urban systems and evaluated the abundance of communities of total heterotrophic bacteria in the water in relation to the monitored physico-chemical factors. The results obtained showed seasonal differences, especially in spring. The high values of the abundance of heterotrophs in winter are related to human activity at the sampling stations. Screening for four types of extracellular hydrolytic enzyme with potential for degradation of organic matter (amylases, lipases, proteases and cellulases) led to the conclusion that lipolytic bacteria were dominant in the studied ecosystems, while proteolytic bacteria were observed in low numbers, but were present in urbanized areas. The presence of cellulolytic bacteria is correlated with the development of macrophytic vegetation. The aim of the present study was oriented towards the evaluation of the anthropogenic input in several lakes surrounding Bucharest in the Nord-Eastern region. These urban ecosystems are generated as a requirement of city development. The microbiological and general enzymatic approaches generated some novel results concerning the pollution degree of aquatic urban ecosystems and could be considered as a platform for further investigation.

Macrophyte Diversity as a Response to Extreme Conditions in the Post-Mining Lakes of the Muskau Arch (West Poland)

The pit lakes localized in the eastern part of the Muskau Arch (Western Poland) developed as a result of lignite mining at the turn of the 20th century. The formation of the lakes varied over time and was determined by many hydrogeochemical and biological factors, which resulted in very diverse ecosystems. Thirty of these lakes were studied in the vegetation seasons of 2016 and 2017. The aim of the study was to identify the main factors influencing the diversity of macrophyte vegetation growing under very extreme and diversified habitat conditions. Therefore, in each lake the numbers of macrophyte species and communities were determined, and the water was characterized by 26 physico-chemical parameters and Chl a. Additionally, the genesis, age, area and maximum depth of each lake was determined. The results showed high diversity of habitat conditions. Based on the physical and chemical water properties, four different clusters of lakes were distinguished. The multiple statistical comparisons showed that the main factors responsible for lake differentiation were pH, water mineralization and to a lesser extent, nutrient concentration and water transparency. The physico-chemical differentiation was reflected in the significant differences in the number of species, number of communities, maximum vegetation extent and amount of chlorophyll-a per lake. The correlational analyses confirmed significant relationships between habitat conditions and macrophyte flora diversity in the lakes. Some macrophyte species were found in very extreme environments not previously reported in the literature. Our results showed that in addition to natural processes affecting species diversity in the lakes, the negative impact of anthropogenic pressures (neutralization and fertilization of the water), which leads to the degradation of their unique character, is also an important factor.

The Biodiversity–Biomass Relationship of Aquatic Macrophytes Is Regulated by Water Depth: A Case Study of a Shallow Mesotrophic Lake in China

The relationship between biodiversity and productivity (or biomass production) (BPR) has been a popular topic in macroecology and debated for decades. However, this relationship is poorly understood in macrophyte communities, and the mechanism of the BPR pattern of the aquatic macrophyte community is not clear. We investigated 78 aquatic macrophyte communities in a shallow mesotrophic freshwater lake in the middle and lower reaches of the Yangtze River in China. We analyzed the relationship between biodiversity (species richness, diversity, and evenness indices) and community biomass, and the effects of water environments and interspecific interactions on biodiversity–biomass patterns. Unimodal patterns between community biomass and diversity indices instead of evenness indices are shown, and these indicate the importance of both the number and abundance of species when studying biodiversity–biomass patterns under mesotrophic conditions. These patterns were moderated by species identity biologically and water depth environmentally. However, water depth determined the distribution and growth of species with different life-forms as well as species identities through environmental filtering. These results demonstrate that water depth regulates the biodiversity–biomass pattern of the aquatic macrophyte community as a result of its effect on species identity and species distribution. Our study may provide useful information for conservation and restoration of macrophyte vegetation in shallow lakes through matching water depth and species or life-form combinations properly to reach high ecosystem functions and services.

The Orava dam reservoir – an important site of aquatic molluscs in north-western Slovakia

Mollusc assemblages of the Orava reservoir, the biggest dam reservoir in Slovakia, were studied in 2020. The reservoir, built in 1941–1953, is situated in north-western Slovakia. Sixteen aquatic mollusc species (13 gastropods, 3 bivalves) were recorded. Valvata piscinalis (O. F. Müller), Radix auricularia (Linnaeus) and Gyraulus parvus (Say) were the most frequent; they were recorded in more than ten sites each. Rich mollusc assemblages, composed mainly of gastropods, were found in sites with rich littoral vegetation of macrophytes. The bivalve diversity and abundance were very small, especially compared to the other studied dam reservoirs. The current results were compared with the previous surveys. The occurrence of Radix lagotis (Schrank) is its first reliable record in Slovakia. Viviparus acerosus (Bourguignat), Aplexa hypnorum (Linnaeus), Anodonta cygnea (Linnaeus), non-native Potamopyrgus antipodarum (Gray) and Physa acuta (Draparnaud) were recorded in this area for the first time and their sites are outside their known range in Slovakia.

Semiaquatic spiders Alopecosa cinnameopilosa rely on prey derived from macrophyte‐based food web: evidence from Lake Izunuma, Japan

Although lacustrine food webs have been extensively studied, food webs formed on floating-leaved macrophytes are poorly understood. In recent years, lotus Nelumbo nucifera, which was often seen in shallow waters, has rapidly expanded and covered a significant part of the surface of the eutrophic shallow Lake Izunuma in Japan. We investigated the diet of the semiaquatic spider Alopecosa cinnameopilosa collected from lotus vegetation and the shore, using carbon and nitrogen stable isotopes. We categorized the spiders’ potential diet as aquatic prey (aquatic insects and small fish), terrestrial insects, or semiaquatic leaf beetles (Donacia provostii and Galerucella nipponensis) that forage mainly on floating-leaved macrophytes. In lotus vegetation, A. cinnameopilosa relied mostly on leaf beetles (mean dietary contribution: 57.3% in July and 46.0% in September). On the lake shore, A. cinnameopilosa relied on both leaf beetles (41.0%) and aquatic prey (36.4%) in July, whereas they relied mostly on aquatic prey (83.1%) in September. The difference in diets between sites could reflect differences between sites in the abundance of leaf beetles. Therefore, macrophyte-based food webs that start from lotus or water chestnuts could significantly support semiaquatic spiders on macrophyte vegetation in Lake Izunuma.

Water level changes in Lake Constance and their relationship to changes in macrophyte settlement in the outflows of Lake Constance Upper and Lower Lake

Since 2008, water level differences between Upper and Lower Lake Constance have increased after they decreased significantly in the 20th century. Questioning the causes leads to the hypothesis that the significant changes in the submerged macrophyte vegetation due to eutrophication and subsequent oligotrophication have played an essential role over the past decades. To clarify whether macrophyte vegetation is the cause of the changed water levels, the spatial distribution of Swiss pondweed Potamogeton helveticus (syn. Stuckenia helvetica) and the other submerged macrophytes was mapped in 2017. Swiss pondweed, in particular plays a key role as a perennial plant type in flow channels. Shoot densities and lengths of this species were recorded by diving. The investigations were supplemented by hydrodynamic modeling of the effects of macrophyte flow resistance on lake water level relationships.The results show that P. helveticus has indeed increased significantly over the past decade. The species colonizes the bottom of flow channels in the Seerhein up to 6 m deep with up to 1000 shoots per square meter and a length of up to 5 m, whereas in the previous decades it only occurred at the edges of flow channels as small stands with shoot lengths of less than 1 m. In the shallow water zones outside the flow channels, stoneworts in particular have spread in the Seerhein over the past decade. The hydrodynamic modeling supports the hypothesis that aquatic plants are the cause of the changed lake water level conditions and illustrate the related changes in the flow velocity field.

The Discovery of the Rare Chara baueri (Charales, Charophyceae) in Serbia.

Chara baueri is one of the rarest charophytes worldwide. It had been considered extinct in Europe for more than a century, from the 1870s to 2006, when it was rediscovered in Germany. The current distribution of this species is limited to a few localities in Europe (Germany, Poland and Russia), and one locality in Asia (Kazakhstan). We present a new finding of Chara baueri, to be a significant contribution to the species ecology and biogeography, and helping to review and update the current scarce knowledge. Chara baueri was discovered in Serbia and monitored for two vegetative seasons in 2018 and 2019, along with the associated macrophyte vegetation and water quality parameters. The morphology and ecology data of the species are presented comparatively with the literature data and the biogeography is critically reviewed. The population in Serbia is the first verified record of Chara baueri in southern Europe. Considering the recent findings and the knowledge accumulated in these records, Chara baueri was very possibly never extinct at all, but overlooked in Europe for the entire 20th century. We suggest that waterfowl migrating from the northern parts of Europe should be considered as the important spreading agent of Chara baueri in southern regions.

Ecology and Partial Restoration of Daha River for Fish Productivity

Daha river, a threatened water body of polluted nature in the Gopalganj district of Bihar was studied for its degradation and possible restoration. The study reveals high rate of sedimentation and agricultural activities, changes in water quality and biotic community. Agricultural activities have led to high input of nitrogen (N) and phosphate (P) fertilizers along with pesticides being used by the farmers. The positives response of restoration practices was observed with partial improvement in fish-productivity due to hindrance factors acting upon severe fish species.The mean concentration of phosphate, nitrate and ammonia corresponds about 0.60-1.40 mg/l, 1.30-2.50 mg/l and 23-43 mg/l in polluted river, while after restoration declines to 0.20-0.48 mg/l, 0.60-1.10 mg/l and 14-27 mg/l, respectively indicating more suitable towards fish productivity. The observations on other water parameters also showed similar trend during partial restoration of Daha river. The cause of algal bloom and other macrophytic population is inorganic ammonia, however, organic pollution is also in polluted state observed as more quantity of ammonia than nitrate especially at site II and Site III during the study period. The concentration of nitrate is much higher than the critical value in polluted river which causes algal diversity and macrophytic vegetation. Therefore, partial restoration of the river helped to enhance fish productivity concluded from this study.

Assessing the Ecological Water Level: The Case of Four Mediterranean Lakes

The ecological water regime in lake water bodies refers to the water levels that enable the fulfillment of the ecosystem’s multiple functions. Therefore, assessing the ecological water regime necessitates the consideration of hydrological, economic, social, and ecological factors. The present research is focused on the assessment of the ecological water level of four Mediterranean natural lake ecosystems, considering their morphological and biological features. Initially, suggestions on the ecological water regime of the studied lakes were made based on an analysis of the lakes’ morphometry. Further, the ecological and biological requirements of the present fish fauna and aquatic macrophytic vegetation were considered. For the latter, mapping was conducted by extensive sampling according to international standards, in order to assess macrophyte composition, abundance, and chorology, as well as species sensitivity to water level fluctuations. The above guided the proposals on the optimal water level regime that should be met by each lake regarding the macrophytic and fish communities’ sustainability, also taking into account the unique hydromorphological features of each lake. The differences in the outcoming results revealed that hydromorphological and biological approaches should be combined for assessing lakes’ ecological water regimes.

Role of saltmarsh production in subsidizing adjacent seagrass food webs: Implications for landscape-scale restoration

Restoration is an increasingly employed method for rehabilitating and enhancing the ecosystem services of lost or degraded coastal habitats, such as supporting high faunal densities and biomass. In certain ecosystems, faunal densities along habitat ecotones are greater than the densities observed in either adjoining habitat, potentially due to the provision of spatial subsidies (e.g., increased food availability). We tested the hypothesis that seagrass-associated consumers immediately adjacent to a saltmarsh are the recipients of food subsidies sourced from saltmarsh primary production. The food web biomarkers we used to evaluate spatial flows of energy across estuarine habitat boundaries included the stable isotope ratios of carbon (δ13C), nitrogen (δ15N), and sulfur (δ34S). We collected primary producers (N = 102) including macrophytic vegetation, benthic microalgae, and epiphytes, as well as 11 key consumers (N = 190) across seagrass meadows either immediately adjacent to (N = 8) or isolated from (N = 8) saltmarsh. We also estimated particulate organic matter (POM) from filter-feeding bivalves and used literature values as proxies for detritus. These food-web biomarkers reveal that seagrass-associated consumers derived 20–23% of basal primary production from the saltmarsh, regardless of saltmarsh proximity. Seagrass sources (epiphytes and vegetation) as well as POM, likely were the dominant contributors for these consumers. This finding indicates that other mechanisms (i.e., refuge provision) might be the primary driver resulting in increased nekton density within seagrass along seagrass-saltmarsh ecotones. While a synergistic restoration of saltmarsh and seagrass habitat may have a positive effect on faunal biomass, it appears there may not be a primary food subsidy benefit to seagrass-associated consumers.

Is there a common threshold to subfossil chironomid assemblages at 16 m water depth? Evidence from the Tibetan Plateau

Fluctuating lake levels are an important driver of ecosystem change, and changes in the precipitation/evaporation balance of a region can lead to undesirable changes in ecosystem functioning. Large-scale changes in hydrology will become increasingly more likely as a result of ongoing climate change in the coming century. This is especially true for the Tibetan Plateau, which plays a crucial role as the “Asian water tower” for the surrounding densely populated regions. Chironomids (Diptera: Chironomidae) have proven to be one of the most valuable bioindicators for monitoring and reconstructing the development of aquatic ecosystems. Besides temperature, water depth and salinity are two of the most important environmental factors affecting chironomids. To study the relationship between chironomids and water depth, we analyzed surface sediment samples of two large Tibetan lakes, Selin Co and Taro Co. These lakes have similar environmental conditions (e.g. elevation, temperature and oxygenation) but show strong differences in salinity (7–10 and 0.5 ppt, respectively). Our results show that the chironomid assemblages in both lakes have similar water depths at which the fauna abruptly changes in composition, despite different faunal assemblages. The most important boundaries were identified at 0.8 and 16 m water depth. While the uppermost meter, the “splash zone”, is characterized by distinctly different conditions, resulting from waves and changing water levels, the cause of the lower zone boundary remains enigmatic. Even though none of the measured water depth-related factors, such as water temperature, oxygen content, sediment properties, light intensity or macrophyte vegetation, show a distinct change at 16 m water depth, comparison to other records show that a similar change in the chironomid fauna occurs at 16 m water depth in large, deep lakes around the world. We propose that this boundary might be connected to water pressure influencing the living conditions of the larvae or the absolute distance to the surface that has to be covered for the chironomid larvae to hatch. We conclude that water depth either directly or indirectly exerts a strong control on the chironomid assemblages even under different salinities, resulting in distribution patterns that can be used to reconstruct past fluctuations in water depths.

Aquatic macrophytes: ecological features and functions

The article is devoted to the analysis of current data on the ecological features and functions of the aquatic macrophytes which are important components of aquatic and wetland ecosystems across the globe. Macrophytes comprise a taxonomically diverse group of macroscopic plants including representatives of vascular aquatic plants, bryophytes, as well as green macroalgae and charophytes. An assemblage of macrophytic vegetation consists of emergent species whose vegetative parts emerge above the water surface, submerged and floating species, with each ecological group having specific features in morphology and physiological processes. A wide range of the adaptive mechanisms developed by aquatic macrophytes at the morphological, physiological, and biochemical levels enables them to inhabit various types of freshwater, brackish-water, and marine habitats. Macrophytes are an important component of aquatic food webs and perform a host of ecological functions in water ecosystems. The main ones are synthesis and storage of organic compounds and oxygen release, absorption and accumulation of chemical elements, water filtration and detoxification of pollutants, release of biologically active compounds involved in interspecies communications, provision of food, shelter and feeding places for aquatic animals, impact on the hydrological regime of water bodies, etc. A wide array of macrophyte species aresed in various human activities, including bioindication of water quality, phytoremediation of contaminated water bodies and wastewater treatment. However, human activities leading to surface water pollution, eutrophication and global warming have led to a concomitant decrease in macrophyte diversity in many freshwater ecosystems and in marine environment. Therefore, proper management of aquatic and wetland ecosystems, including their monitoring and control, is a prerequisite for a successful conservation of habitats and species richness of the aquatic macrophytes.

Estimating the change in regional scale distribution of seagrass and macroalgal beds using discrete local distribution data analyzed from aerial images

AbstractThe sensitivity of vegetated habitats to climate change and catastrophic disturbance, as well as their benefits to human beings, motivate efforts to estimate regional changes in distribution. This study examined the regional changes in the distribution of submerged macrophyte vegetation using aerial and satellite images from before and after the 2011 tsunami disturbance along the Pacific coast of northeastern Japan. We conducted an estimation of the change in the distribution of seagrass and macroalgal beds after the tsunami along the whole coastline (1,635 km). This was based on vegetation change in the 13 local areas (each <40 km) spanning 27% of the coastline and included 28% of the macroalgal area and 59% of the seagrass area documented in satellite imagery before the tsunami, using generalized linear modeling (GLM). We found that in the 13 local areas 716.8 and 1,990.3 ha of macroalgal beds and seagrass beds had disappeared, respectively, suggesting that seagrass beds were more impacted by the tsunami than macroalgal beds. Significant predictors in GLM indicated that more seagrass beds disappeared in geographically complex coastal areas, whereas macroalgal beds were only marginally affected in such areas. It was estimated that the total decline in seagrass beds was at least 76% along the whole coastline, whereas macroalgal beds decreased only by about 20%. The magnitude and predictors of losses in these two vegetated habitats were similar to earlier estimates, suggesting that our simplified method with GLM is sufficient to extrapolate monitoring data to a regional scale.

A high-resolution climate history of geochemical and biological proxies from a tropical freshwater wetland located in the Kenyan Rift Valley

The sedimentary and biological material preserved in wetlands in semi-arid regions provide a rich repository of paleoclimate and paleoecological archives. These records reflect an underutilized, but typically ignored paleoenvironmental resource in semi-arid settings. The results presented here demonstrate that groundwater-fed wetlands constitute a valuable record of environmental change that not only complement reconstructions from lacustrine settings, but also contribute unique data and insights into climate and landscape change.We use data obtained from sediment cores collected from Loboi wetland, a groundwater-fed wetland located in the Equatorial East African Rift Valley of Kenya, to demonstrate the value of paleoenvironmental datasets extracted from wetland archives. This article relates surficial sedimentary geochemical data (TOC, δ13C, δ15N, C:N, and %C3) at Loboi to the extant macrophytic vegetation. The surficial data are used as an analog to interpret the geochemical signature of three sediment cores and a soil pit. The stratigraphic records show significant variation along a north to south transect through the wetland. The geochemistry indicates that papyrus wetland records are distinctly different from Typha dominated wetland sedimentary signatures. The interpretation of the stratigraphic material is further improved by the inclusion of sub-fossil macrophyte and testate amoebae remains. The extraction and identification of seeds of wetland plants from the sedimentary archive provide invaluable genus to species specific details of wetland ecology. Further, the inclusion of testate amoebae as an indicator of surface hydrological conditions has significantly improved interpretation of the hydrological history of Loboi wetland.The stratigraphic record from Loboi indicates that between ~1100 and 1470 C.E. (Medieval Climatic Anomaly) dry conditions dominated the Loboi region, except for a brief period of wetter conditions between ~1275 and 1345 C.E. Seasonally wetter conditions began to persist between ~1470 and 1630 C.E. Wetland sediments developed after this time as reflected by the sequestration of carbon in the sedimentary record. Recent historic biological and sedimentary proxies reflect increased agrarian impacts on the landscape surrounding Loboi.

Experimental evidence for the decline of submerged vegetation in freshwater ecosystems by the invasive Chinese mitten crab (Eriocheir sinensis)

The Chinese mitten crab (Eriocheir sinensis) is a damaging invader which is designated as a species of Union Concern within the European Union. A negative impact of the crabs on macrophyte vegetation in lowland rivers is suspected but not yet proven or quantified. We have performed a mesocosm study that combines a density gradient of Chinese mitten crabs (0, 0.3, 1.0 and 2.5 ind. m−2) with chemical stress (2350 µg EDTA L−1 + 258 µg glyphosate L−1) or light limitation stress (− 70% irradiance compared to control) on water plants (Myriophyllum spicatum). The results clearly demonstrate that the crabs are capable of removing plant shoots effectively which can lead to a complete elimination of the vegetation. Generally, the higher the crab density, the sooner the plants started to disappear and the sooner the vegetation was completely removed. Additional light and chemical stress accelerated this process: plant disappearance at a crab density of 0.3 ind. m−2 compared to 1.0 ind. m−2 in the control treatments. Video recording, plant strength and crab pinch strength measurements and stable isotope signatures of δ13C and δ15N in the Chinese mitten crabs and their possible food sources showed that directly eating the plants is causing only minor damage to the plants. Most damage comes from the movement of the crabs and crab–crab interactions during which they use their chelae to grasp the shoots. We conclude that a decline of vegetation as a consequence of Chinese mitten crab behaviour can be a realistic scenario in freshwater ecosystems and warrants close attention and monitoring. Being primary producers and ecological engineers, macrophytes are key species in these ecosystems, whose services are lost when they disappear and are difficult to restore.

Movements, habitat use, and entrainment of stocked juvenile lake sturgeon in a hydroelectric reservoir system

Identifying movement and habitat use patterns is essential for fish passage efforts and the conservation of threatened species. We used acoustic telemetry to track the movements of 44 juvenile lake sturgeon (Acipenser fulvescens) throughout Kleber Reservoir in northern Michigan. On average, lake sturgeon moved 502 m between telemetry positions, with age-2 lake sturgeon moving longer distances than age-1 lake sturgeon. Areas with high numbers of lake sturgeon detections were clustered near the forebay, while zones with low numbers of detections were clustered toward the head of the reservoir. Analyses showed that 66.4% of the variance in habitat use could be explained by physical habitat features. Reservoir areas with ample deepwater habitat, fine soft substrates, and limited macrophyte vegetation were the most frequently occupied and, thus, may provide suitable habitat conditions to support juvenile lake sturgeon. We observed that 54.4% of the age-1 and 52.8% of the age-2 lake sturgeon stocked into Kleber Reservoir were entrained. Reservoir size, morphology, and the location of suitable habitat in relation to hydroelectric infrastructure may be key factors that affect entrainment rates.

Patterns of distribution and drivers of change in shallow seagrass and algal assemblages of a non-estuarine Southern Caribbean mangrove lagoon

Shallow marine macrophyte communities serve key roles in the tropical coastal ecosystem but are undergoing large and rapid deterioration worldwide, as is also the case in the non-estuarine mangrove lagoon of Lac Bay, Bonaire, in the Southern Caribbean. To help better understand both the drivers of assemblage structure and potential consequences of the changes taking place in the bay, we here quantify and describe the distribution of algal and seagrass assemblages along the environmental gradient from the turbid, inner mangrove pools to the clear, open bay conditions, based on 98 randomly-chosen, 4 m2 survey plots. Seven assemblages were described along this land-to-sea gradient, five of which were dominated by marine macrophytes, one by sponges and one by a polychaete. With exception of the hypersaline backwaters which were devoid of benthic macrophyte vegetation, isolated mangrove pools showed the lowest total benthic cover, species richness and biodiversity of all habitats. Salinity and substrate particle-size composition accounted for most variation between the different assemblages and appear to be the key known determinants of assemblage composition. We developed a conceptual model to help disentangle the relationship between and the relative roles of the two principal drivers, as part of a cascade of effects which ultimately result from terrestrial run-off into the bay as mediated by mangrove encroachment into the bay. The model links spatial patterns to ongoing processes and implies that the assemblage patterns described are not only a reflection of, but also allow prediction of how the assemblages develop through time.

Nitrogen retention efficiency of a surface-flow constructed wetland receiving tile drainage water: A case study from north-eastern Germany

A surface-flow constructed wetland to retain nitrogen was created between an agricultural tile-drainage plot and the outflow-receiving river in a maritime rural area of north-eastern Germany close to the southern Baltic Sea. The nitrogen loads were monitored from October to May over a period of four years at the inlet and outlet using high-frequency water sampling and flow measuring to assess the performance of the wetland. The effects of the physical boundary conditions on the nitrogen retention processes were analyzed by measuring meteorological indicators and water temperatures in the wetland as well as by a detailed mass balance calculation. The development of vegetation and the sedimentation of carbon and nitrogen in the wetland were also recorded. The results showed that the nitrogen retention efficiency of the wetland decreased with increasing nitrogen loading, while it increased with increasing residence times and temperatures. We conclude that the hydraulic retention time should be >20 days and the water temperature should be >8 °C in order to be able to effectively retain nitrogen. However, both conditions were only met from spring to autumn. In these periods, the development of dense, structure-rich macrophyte vegetation and the sedimentation of carbon and nitrogen quickly provided good conditions for nitrogen retention. In autumn and spring, however, less than 20% of the annual nitrogen load was observed. The total nitrogen loading was reduced by only 2.9% during the four monitored years. The study results suggest that the meteorological and hydrological conditions were not conducive to achieve a significant nitrogen retention with the help of surface-flow constructed wetlands in this climatic region. The successful implementation of wetlands in the maritime rural area close to the Baltic Sea should therefore consider the inner-annual distribution of the outflows from the tile drainage plot.

Temperature and salinity effects on submerged aquatic vegetation traits and susceptibility to grazing

Submerged macrophyte vegetation provides valuable ecosystem services, but climate- and management-driven changes may alter plant traits in unexpected and interactive ways. Further, such changes in plant traits may influence herbivore response, with feedback to bed characteristics. We manipulated temperature (20, 25, 30 °C) and salinity (0, 6, 12) in mesocosms to simulate current and predicted scenarios for the San Francisco Bay area. We measured traits of Stuckenia pectinata (sago pondweed) and subsequent effects on invertebrate (amphipod, Ampithoe valida) grazing. Counter to predictions, higher temperatures tended to have positive effects on plant traits (leaf area, aboveground biomass, nitrogen [N], phosphorus [P], protein, and total phenolic content). Also, unexpectedly, the highest salinity treatment had few negative effects except when temperature was coolest; i.e., 20 °C and a salinity of 12 led to decreased carbon [C], N, P, protein, phenolic concentrations, and aboveground biomass. Conversely, the highest salinity (12) at the highest temperature (30 °C) produced the highest leaf N and P, and plants from this treatment suffered most from herbivory. Consumption rates significantly increased with lower leaf fiber and higher total leaf N and protein content; i.e., plants with more nutritious leaves and less structural defense were consumed most. Climate change is expected to increase both salinity and temperature, but manipulation of freshwater supply could lead to decreased salinity. The range of responses in S. pectinata traits and invertebrate grazing shown by our results imply that the specific combination and magnitude of human influences will differentially shape these submerged macrophyte beds and their functions.