Ecological classification of macroalgae and angiosperm communities of inner coastal waters in the southern Baltic Sea

A classification system of macroalgae and angiosperms for the inner coastal waters of the Baltic coast of Mecklenburg-Vorpommern (Germany) was developed according to the guidelines of the European Water Framework Directive. These guidelines ask for a five-step classification scheme (high, good, moderate, poor, bad) of the ecological state based on submerged macrophytes.The approach is based on the comparison of the occurrence and distribution of plant communities in 1999–2003 with historical data of submerged macrophytes and their community structure. Due to the lack of appropriate data, historical depth distribution limits of plant communities were calculated based on modelled historical underwater light climate.Despite the fact of very heterogeneous salinities (0.5–20.0 practical salinity units, psu) and substrate types (silty–sandy) in the study area, two general main criteria were identified as appropriate indicators of eutrophic degradation of the inner coastal waters: (1) the lower distribution depth of plant communities and (2) the loss of charophyte-dominated plant communities. Based on these two criteria, a five-step classification scheme is proposed for the characterisation of the ecological state. The depth limit boundaries between the ecological classes were calculated by 5, 25, 50 and 75% reduction of the water transparency. Based on this calculation, the ecological status is described by the gradual upward shift of the vegetation depth limit. Complementary to the decrease of depth limits the loss of charophyte-dominated plant communities characterises the border between moderate and poor ecological conditions.     

An experimental system to study ecophysiological responses of submerged macrophytes to temperature and light

An experimental growth system was devised to study the ecophysiological responses of submerged macrophytes to temperature and light. Using the system, a pilot study was conducted to compare responses to light of three representative species common to the littoral zone of Lake Biwa: Vallisneria asiatica Miki var. biwaensis Miki, which is endemic to Japan, Potamogeton maackianus A. Benn., a dominant submerged macrophyte in Lake Biwa, and Elodea nuttallii (Planch.) St. John, one of the most influential submerged exotic macrophytes naturalized in Japan. Different relative growth rate responses and other growth parameters among the species were observed. We ascertained the experimental system to be useful for the comparison of ecophysiological responses of submerged macrophytes.     

Assessing maximum depth distribution,vegetated area,and production of submerged macrophytes in shallow,turbid coastal lagoons of the southern Baltic Sea

Submerged macrophytes improve water quality in shallow coastal lagoons but eutrophication often resulted in a degradation of macrophytes. Management measures that protect and restore macrophyte stands require knowledge on what limits macrophyte distribution. Information on macrophyte production and distribution in the Darss-Zingst Bodden Chain (southern Baltic Sea) is lacking since an almost complete loss of submerged vegetation in the 1980s. Nutrient input was reduced in the 1990s and macrophytes seem to recover, although turbidity is high and light conditions are still poor. However, this recovery raised hope that returning macrophytes could stabilize sediments and improve water clarity. In this study, seasonal changes in photosynthesis–irradiance curves of selected macrophyte species were used to calculate potential primary production in different depths and turbidity situations. Bathymetry of the area is then used to assess depth distribution and vegetated area. Since the so-calculated depth limits correspond well with the actual depth distribution in the field, macrophyte depth distribution is concluded to be mostly determined by light conditions. Most macrophytes grow in very shallow areas up to 50 cm depth where also 70% of potential primary production takes place. Present light conditions do not support a further expansion of macrophyte distribution in the DZBC.     

Depth distributions of Fucus vesiculosus L. and Zostera marina L. as classification parameters for implementing the European Water Framework Directive on the German Baltic coast

A classification approach was developed within the European Water Framework Directive for the outer coastal waters of the German Baltic Sea. We concentrated on the known recent presence and depth distribution of Zostera marina and Fucus vesiculosus along the German coast. According to the European Water Framework Directive the reference conditions were reconstructed based on historical data. The available databases indicate that both species formerly occurred down to 10 m depth along the whole German Baltic Sea coastline, independent on the salinity gradient. The recent depth distribution of Z. marina varied between 2.5 and 7.9 m along the German Baltic coast. Dense F. vesiculosus stands were observed only along the western part of this coast at a maximum depth of 4.7 m. Comparing the historical data sets with recent findings reveals a strong decline of depth limits for both species during the last century. Therefore, we used both species to describe the degradation of the Baltic Sea coastal waters using change in the depth distribution. The boundaries of the ecological status according to the Water Framework Directive were calculated based on modelling. Ecophysiological light demands of species and decrease of water transparency (light reduction in percent) were used to describe the degradations. This approach is robust against variation of macrophyte light requirements and is straightforward to classify recent long-term macrophyte monitoring. However, it is very sensitive against changes in the depth distribution and may result in erroneous estimations of ecological class boundaries when insufficient historical data are used as reference. This model allows the adaption of the boundaries calculations to new knowledge about historical data and ecophysiological light demand of plants. Actually, the boundaries of the classification were defined as follows: 1% light reduction represents the transition from high/pristine to good ecological status, and 5% indicates the transition from good to moderate status. At least 25% reduction corresponds to a poor status, more than 75% to a bad status.     

基于水下光照条件和种子库分布指示沉水植物恢复区:以金湖为例

研究以湖北枝江金湖(由东湖和刘家湖组成)为例,综合水下光照条件和沉水植物种子库分析,探讨沉水植物可恢复区的判别方法。研究分别于2018年6月和12月对金湖开展了综合调查,并在6月开展了种子库调查。结果表明,金湖富营养化问题较严重, 6月各位点水深-透明度比值均低于沉水植物生长的阈值需求,范围为0.13—0.25,平均为0.17; 12月部分位点的水深-透明度比值达到了沉水植物生长的阈值需求,范围为0.18—0.95,平均为0.44。各位点沉水植物种子库密度范围为0—200 ind./m²,平均为24 ind./m²。根据金湖的水下光照条件和沉水植物种子库分布情况,结合湖底地形,建议在冬春季透明度较高的时期降低水位,进行沉水植物恢复工作。通过水下地形、光照条件和种子库的综合分析,对金湖的沉水植物恢复区进行了划分,结果显示东湖的东南部、东湖的西岸、刘家湖的西部和东岸作为沉水植物恢复区较为合适。该研究有望为湖泊沉水植物的恢复提供定量化的参考建议,提高生态修复工程效果和降低管理成本。     

洱海沉水植物的光合特性与分布水深的关系

为研究沉水植物光合特性与其分布水深的关系,选取黑藻(Hydrilla verticillata)、苦草(Vallisneria natans)、水蕴草(Egeria densa)、大茨藻(Najas marina)、微齿眼子菜(Potamogeton maackianus)、光叶眼子菜(Potamogeton lucens)和穿叶眼子菜(Potamogeton perfoliatus)等15种洱海常见沉水植物,测定其光合作用参数。结果表明:光合速率为2.8—18.1μmol O₂/(g DW·h)、暗呼吸速率为0.3—2.0μmol O₂/(g DW·h)、光补偿点为6.3—63.8μE/(m²·s)、光饱和点为55.6—441.5μE/(m²·s),不同沉水植物间光合作用参数存在显著差异。结合洱海全湖沉水植物分布水深调查结果,沉水植物的光补偿点和光饱和点与分布水深呈显著负相关;苦草与其他物种比较具有更低的光补偿点6.3μE/(m²·s)、光饱和点55.6μE/(m^2...     

Depth limits and minimum light requirements of freshwater macrophytes

1. Data for maximum colonization depth (Z_c) of five groups of submerged macrophytes and light attenuation were collected for forty-five Danish lakes and 108 non-Danish lakes. The macrophyte groups were bryophytes, charophytes, caulescent angiosperms, rosette-type angiosperms and Isoetes spp. 2. The data showed systematic differences among the groups in the relationship of Z_c to water transparency. In lakes with low transparency (Secchi disc transparency (Z_s) less than 7 m) caulescent angiosperms and charophytes penetrated deepest followed by bryophytes and Isoetes spp. In more transparent lakes bryophytes grew deepest, followed by charophytes, caulescent angiosperms and Isoetes spp. Rosette-type angiosperms had the lowest Z_c in all types of lakes. Charophytes and caulescent angiosperms had similar depth limits in lakes with Z_s < 4 m but charophytes grew deeper in more transparent lakes. The depth limits of both groups were independent of light penetration in lakes with very low transparency (Z_s < 1 m). The annual light exposure for the deepest growing macrophytes (bryophytes) was 20–95 mol photons m^–2. 3. The relationship between Z_c, macrophyte type and lake transparency could be explained by three distinct processes regulating Z_c. In lakes with low transparency (Z_s < 1 m), tall macrophytes (caulescent angiosperms and charophytes) compensate for light limitation by shoot growth towards the water surface and Z_c is therefore independent of transparency. In lakes with medium transparency (1 m < Z_s < 4 m) Z_c for angiosperms, charophytes and Isoetes spp. is constrained by light attenuation in the water column, corresponding to a linear relationship between Z_c and Z_s. This pattern also applies to bryophytes, despite lake transparency. In transparent lakes, the minimum light requirement at Z_c increased with increasing transparency for angiosperms, charophytes and Isoetes spp. 4. The minimum light requirements among submersed macrophytes (including marine macroalgae) depend on their plant-specific carbon value (plant biomass per unit of light-absorbing surface area) for the species/group, indicating that the light requirements of submersed plants are tightly coupled to the plants’ possibility to harvest light and hence to the growth form. 5. The light requirements increased on average 0.04% surface irradiance per degree increase in latitude corresponding to an average decrease in Z_c of 0.12 m per degree latitude.     

Temperature and light: The determining factors in maximum depth distribution of aquatic macrophytes in Ontario,Canada

In stratified lakes with high light penetration, the maximum depth at which macrophytes occur is frequently limited by temperature. At this depth a variety of species may be found. On the other hand, when the clarity of water limits the light penetration and the temperature at depth is sufficient for good plant growth, the plants occurring at greatest depth are ones that do not require photosynthetic oxygen for root growth. Such plants include the Charales, Isoetes, Utricularia and Ceratophyllum.     

The ecological performance of metallophyte plants thriving in geochemical islands is explained by the Inclusive Niche Hypothesis

Aims The Inclusive Niche Hypothesis has not been validated for plants using ecophysiological performance. The few experiments have measured growth and competition but not the physiological response of plants. A metallophyte plant that hyperaccumulates aluminium (Al), Plantago almogravensis, showed a defined spatial distribution by occurring mostly on vegetation gaps associated with metalliferous areas (geochemical islands). This case was used to determine, in situ, whether the Inclusive Niche Hypothesis was suitable to explain the extent of the species realized niche.Methods The vegetation associated with P. almogravensis geochemical islands in the SW coast of Portugal was mapped. The biotic (neighbouring plants) and abiotic (edaphic) components of the niche were correlated with parameters of the plant's ecological and physiological performances (plant density and cover; leaf C and N concentration and isotopic composition; growth). The results were obtained using image analysis, abundance and morphological measures, isotopic signatures and chemical composition.Important findings The species showed better physiological performance where its ecological performance was lower due to trade-offs with environmental constraints. The species' realized niche was mostly limited by shrub competition and soil Al-toxicity. These limits contribute to explain the rarity status of the species: the species has a poor capacity to compete but, due to an enhanced Al-tolerance and Al-hyperaccumulator trait, has the ability to find refuge in geochemical islands that are too harsh for most other species. This work, based on ecophysiological field studies, provides support for the Inclusive Niche Hypothesis relating to plant species.     

Littoral zone macrophyte community structure: Distribution and association of species along physical gradients in Lake George,New York,U.S.A.

The distributional patterns of 38 species of submersed macrophytes were studied at 50 sites in the littoral periphery of Lake George, New York. Density measurements (plants per square meter) for each species at depths of 1, 2, 3, 5, 7 and 9 m were determined at transects at each site and converted to midsummer shoot biomass estimates (grams dry mass per square meter). These data were then analyzed in terms of 13 different physical, chemical and biological variables to evaluate probable major factors controlling distribution within the lake. Ordination and factor analysis indicated that depth, substrate type and eutrophication status were primary correlative factors. Four major depth classes were evident from cluster analysis of presence-absence data: shallow water, deep water, and cosmopolitan, both with and without preference for deeper waters. Cluster analysis also identified the co-occurrence of several plant species. Geographical grouping of the 50 sites into the various basins of the lake demonstrated important compositional trends in species diversity and dominance within the lake itself. The competitional strategies, ecological requirements and species characteristics are described.     

Hundred Years of Environmental Change and Phytoplankton Ecophysiological Variability Archived in Coastal Sediments

Marine protist species have been used for several decades as environmental indicators under the assumption that their ecological requirements have remained more or less stable through time. However, a growing body of evidence suggests that marine protists, including several phytoplankton species, are in fact highly diverse and may quickly respond to changes in the environment. Predicting how future climate will impact phytoplankton populations is important, but this task has been challenged by a lack of time-series of ecophysiological parameters at time-scales relevant for climate studies (i.e. at least decadal). Here, we report on ecophysiological variability in a marine dinoflagellate over a 100-year period of well-documented environmental change, by using the sedimentary archive of living cysts from a Scandinavian fjord (Koljö Fjord, Sweden). During the past century, Koljö Fjord has experienced important changes in salinity linked to the North Atlantic Oscillation (NAO). We revived resting cysts of Pentapharsodinium dalei preserved in the fjord sediments and determined growth rates for 18 strains obtained from 3 sediment core layers at salinity 15 and 30, which represent extreme sea-surface conditions during periods of predominantly negative and positive NAO phases, respectively. Upper pH tolerance limits for growth were also tested. In general, P. dalei grew at a higher rate in salinity 30 than 15 for all layers, but there were significant differences among strains. When accounting for inter-strain variability, cyst age had no effect on growth performance or upper pH tolerance limits for this species, indicating a stable growth response over the 100-year period in spite of environmental fluctuations. Our findings give some support for the use of morphospecies in environmental studies, particularly at decadal to century scales. Furthermore, the high intra-specific variability found down to sediment layers dated as ca. 50 years-old indicates that cyst-beds of P. dalei are repositories of ecophysiological diversity.     

The importance of seasonal macrophyte cover for the behaviour and performance of brown trout (Salmo trutta) in a groundwater‐fed river

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Determining critical light and hydrologic conditions for macrophyte presence in a large shallow lake: The ratio of euphotic depth to water depth

Light determines macrophyte distribution, community composition and biomass in shallow lakes. Therefore, it is vital to determine the critical underwater light climate thresholds for macrophyte degradation and recovery. In this study, we first proposed a novel index, defined as the ratio of euphotic depth (Z_eu) to water depth (WD), as a measure of the underwater light supply for macrophytes. The underwater light environment in Lake Taihu (a large, shallow, eutrophic lake) was then characterized based on this index (Z_eu/WD) using field measurements collected from 2006 to 2013 (8 years × 4 seasons × 32 sites). The distribution of the macrophyte presence frequency (MPF, the number of investigations that identified macrophytes divided by the total number of investigations) was greater than 0.70 in Xukou Bay and East Lake Taihu over the 32 investigations, followed by the other sites distributed in East Lake Taihu. The proportion of macrophyte coverage increased with the increase in Z_eu/WD. A significant relationship was observed between Z_eu/WD and MPF for the 19 sites with macrophytes (r² = 0.48, p < 0.001, n = 19). In the region with high nutrient concentrations and serious water pollution, better underwater light conditions are required for the growth of macrophytes. A Z_eu/WD value of 0.80 can be regarded as the critical underwater light threshold for the growth of macrophytes in Lake Taihu. The region with Z_eu/WD ranging between 0.57 and 0.80 was usually covered by sparse macrophytes; this region should be vital for macrophyte recovery and environmental management in Lake Taihu. The distribution of Z_eu/WD was further obtained using MODIS satellite-derived Z_eu from June to October in 2003 and 2013. Xukou Bay and Guangfu Bay in the southern part of Lake Taihu could be regarded as potentially crucial regions for the recovery of macrophytes from the perspective of underwater light and nutrient levels.     

Assessing ecological quality of shallow lakes: Does knowledge of transparency suffice?

The European Water Framework Directive (WFD) requires that all aquatic ecosystems in their member states should reach ‘good’ ecological quality by 2015. To assess ecological quality, the WFD requires the definition of reference conditions using biological, physical and chemical indicators and the assignment of each water body to one of five quality classes using these indicators. Elaborate assessment schemes using large sets of variables are now being developed. Here we address the question whether all this is really needed and what the simplest assessment approach would be for the case of shallow lakes. We explore the relationships between the quality class assigned to a lake by experts in shallow lake ecology and a rich set of biological, physical, and chemical data. Multinomial logistic regression analyses were carried out based on data from 86 shallow lakes throughout Europe that were sampled in 2000 and/or 2001. Ecological quality of shallow lakes judged by experts was strongly correlated to physical and chemical variables associated with light regime and nutrients and much less to biological variables.Our regression model showed that ecological quality of this set of shallow lakes judged by experts could be predicted quite well from water transparency expressed as Secchi depth and that other variables did not contribute to it significantly. According to the WFD, lakes should at least have a ‘good’ ecological quality. Quality judged by experts and predicted quality were similar for 78% of the lakes with respect to meeting this standard. As a cautionary note we stress that Secchi depth alone will be a less useful indicator if effects of stressors other than eutrophication (e.g. lake acidification and toxic pollution) are to be considered.     

Drivers of macrophyte development in rivers in an agricultural area: indicative species reactions

The ecological drivers of macrophyte development in a lowland agricultural area were tested based on a 2008 survey on the Wkra River catchment. Our survey was carried out in the rivers of an agricultural area with relatively high concentrations of both nitrates and phosphates in the water. By using the Polish macrophyte method, we were able to calculate several botanical metrics. Canonical ordination analyses used to relate biological data to environmental variables such as physical and chemical parameters of water, surface water velocity or river width, were carried out using CANOCO for Windows. Redundancy analysis (RDA) showed that pH and alkalinity were the parameters best correlated with the distribution of macrophytes and values of macrophyte indices. The recorded values of the Macrophyte Index for River in the Wkra River and its tributaries reflected their good and moderate ecological status (the Water Framework Directive scale). Despite the fact that nutrient concentrations in the water were relatively high and that most of the sites represented eutrophic conditions, the results of this survey showed that non-nutrient parameters may play an important role in explaining aquatic plant occurrence in rivers that have been subjected to eutrophication.     

Effects of anthropogenic salinisation on the ecological status of macroinvertebrate assemblages in the Werra River (Thuringia, Germany)

For more than 100?years, the Werra River has been severely affected by intensive salinisation caused by potash fertilizer industries. We show considerable differences in macroinvertebrate assemblages between reaches without salinisation impact and downstream reaches with intense anthropogenic salinisation in the Werra. This is true for almost all biological metrics relevant for ecological status classification under the EU-Water Framework Directive (EU-WFD) (European Community, Directive 2000/60/EC of the European Parliament and of the Council of 23 October 2000 establishing a framework for Community action in the field of water policy, No. L 327/1, of 22 December 2000) and diversity measures (taxon richness, evenness). Macroinvertebrate assemblages at salinisation sites were completely dominated by three halophile neobiotic macroinvertebrate species (Gammarus tigrinus, Corophium lacustre and Potamopyrgus antipodarum). We compared anthropogenically salinised sites from the Werra with disturbed but non-salinised sites from the Werra and other German rivers. We used biological metrics developed for classifying the ecological status according to the EU-WFD. This comparison indicated a severe degradation at salinisation sites on the Werra and these fell into the worst ecological status class ??bad?? according to the EU-WFD. Multivariate statistical analyses revealed anthropogenic salinisation as a key factor causing the differences in composition of macroinvertebrate assemblages in the Werra between salinisation and reference sites. Analyses of the long-term presence?Cabsence data of macroinvertebrate assemblages indicated no marked improvement in the ecological status in the past 20?years.     

沉水植物功能性状研究的思考

植物的功能性状是指植物体具有的与生长、存活和繁殖紧密相关的一系列核心植物属性,这些性状通常有非常重要的生态学意义。目前,基于植物功能性状的研究已经快速扩展到生态学研究的众多领域。沉水植物是一类与水环境关系密切的生态类群,对浅水湖泊生态系统的结构和功能有重要的意义。之前对功能性状研究主要集中在陆生木本植物,尚无对沉水植物（沉水草本）功能性状的综述。本研究根据沉水草本与陆生植物功能性状的差异,基于陆生植物功能性状研究中的几个重要问题对现有沉水草本植物功能性状的研究进行归纳和梳理。最后对未来沉水植物功能性状的研究方向进行了展望,提出在当前全球气候变化背景下,功能性状研究也可用于指导淡水生态系统的修复。     

The influence of light environment on depth of visual feeding by larvae and fry of Coregonus pollan (Thompson) in Lough Neagh

The depth limits for visual feeding by pollan larvae and fry, Coregonus pollan , were determined in Lough Neagh, Northern Ireland, by combining laboratory estimates of the minimum light threshold for feeding activity with field measurements of spectral, diurnal and seasonal changes in light penetration. Although feeding thresholds were lowest in the blue light (400–490 nm), the rapid attenuation of this region in the lake meant that the depth limits of feeding in situ were determined by response to the green region (490–595 nm). Effects of changes in irradiance and light penetration on the depth of feeding are considered during a seasonal study. Increased sensitivity, as the juvenile stages develop, may be offset by reduced light penetration due to algal growth. Over an annual period the maximum feeding depth for pollan varied between 2.6 and 4.1 m. In the juvenile stages of two other predatory species from the lake, perch, Perca fluviatilis , and pike, Esox lucius , the corresponding ranges were 1.1–1.9 m and 2.7–4.6 m respectively.     

Prediction of potential macrophyte development in response to restoration measures in an urban riverine wetland

Wetland restoration efforts require practical models for predicting the effects of various measures on ecosystem structure and function. The present study examined the species diversity and abundance of macrophytes in relation to hydrological parameters in the Alluvial Zone National Park along the Austrian Danube with a main focus on the Lobau, an urban riverine wetland within the city limits of Vienna. A macrophyte regression model was developed based on the output of a 2D hydraulic model for different wetland management options. These management options describe possible rehabilitation measures by re-connecting the riverine wetland with the Danube. Stepwise multiple regressions revealed that the most important predictors of macrophyte diversity and abundance were water velocity at bankfull discharge (maximum water velocity) and size of shallow water areas (<1 m depth) during the growing season. Macrophyte abundance and diversity increased with decreasing water velocity and increasing shallow water area. These parameters integrate information about environmental features such as nutrients, light availability and hydrological disturbance for macrophytes and explained between 65 and 85% of the macrophyte distribution in an analysis. The model results enabled us to predict quantitatively the development and spatial distribution of macrophytes for different management options in this urban riverine wetland. These predictions suggest that partial reconnection could be a compromise solution at the scale of the whole riverine wetland, increasing the availability of suitable aquatic habitats and diversifying the types of existing wetland water bodies to establish potential new habitats for macrophyte species.     

Death of submerged macrophytes—Actual field observations and some implications

Using a photographic sampling method, the spatial distribution of dead submerged macrophytes was investigated in lakes Tyrifjord and Steinsfjord, in South Norway. Death incidents were observed in less than 5% of the samples (N = 3257). Distributed sites with unstable sediments had dead plants occuring at all depths, whereas at normal sites, the incidence of dead plants was higher towards deeper waters. In this case, the estimated mortality rose sharply, close to the lower limits of depth extension for the annual Najas flexilis (Willd.) R.&S. and the perennial Isoëtes lacustris L.The statistical analysis of death incidence for the predominant macrophyte Isoëtes lacustris showed that neither depth nor light intensity accounted adequately for the observed deep-water mortality increase. However, probit-transformed mortality correlated significantly (P < 0.001) to a hazard function, derived from light threshold statistics. Mortality magnitude was sufficient to explain the observed steep deep-water decline of I. lacustris. It is concluded that the commonly-observed double-exponential depth decline of submerged macrophytes could well be invoked by light-induced mortality.