Carbon and nutrients transfer from primary producers to lake sediments – a stoichiometric approach

Authors

Lech Kufel, Małgorzata Strzałek, Elżbieta Biardzka, Marcin Becher

We aimed to demonstrate different input of organic and inorganic carbon, nitrogen and phosphorus from three main groups of primary producers (phytoplankton, charophytes and vascular submerged macrophytes) to respective lake sediments. Studies were carried out in one eutrophic and two mesotrophic lakes. Samples of sediments were taken from profundal and from littoral zones, the latter divided into such overgrown by charophytes and others covered by vascular submerged macrophytes. We applied a stoichiometric approach to illustrate variable functional carbon to nutrients relationships. Among profundal sediments, the lowest organic to inorganic carbon ratio was found in sediments from the eutrophic lake due to precipitation of calcium carbonate during algal blooms. Extremely low inorganic carbon input to profundal sediment of one of the mesotrophic lakes may be explained by low phytoplankton production but also by dissolution of once deposited calcium carbonates. Charophyte-dominated littoral sediments contained significantly more inorganic carbon than other littoral and profundal sediments. Comparison of stoichiometric ratios between plant standing crop and underlying littoral sediments showed significant enrichment of sediments in nitrogen manifested by reduction of organic carbon to total nitrogen ratio during plant decomposition taking place both in charophyte and in vascular plant stands. We also attempted to divide phosphorus pool in sediments into organic P and calcium-bound P present in charophyte stands and in profundal sediments of eutrophic lake. In the former, calcium-bound P was estimated at 17–19% of the total P pool while in profundal sediments it amounted 42% of the total P. This difference suggests that calcium carbonate settling during algal blooms in a eutrophic lake may be more effective in P trapping than calcite encrustations covering charophyte plants in littoral sites. In conclusions, we underline the need of considering often neglected inorganic fractions of carbon and phosphorus to get better insight into carbon and nutrient burial in lake sediments.

Responses of lake macrophyte species and functional traits to climate and land use changes

Authors

Ji Yoon Kim, Jun Nishihiro

Aquatic plants are essential components in the regulation of microhabitat complexity and physico-chemical parameters in lake ecosystems. Increased eutrophication, land use change, modification of hydrological regimes, and expansion of invasive species are expected to impact aquatic plant community composition; however, historical pathways and response patterns are not well understood at the national scale. We analyzed temporal changes in aquatic plant communities in Japan from the early 1900s to the 2000s using field survey records from 248 lakes. Relationships of species associations with climate, land use, and lake characteristics were described using a joint species distribution model. The mean variation attributable to lake characteristics was 25.4%, followed by climate (14.0%), and land use (10.5%). Among the 13 functional traits used in our analysis, sexual and pollination traits showed marked responses to precipitation and land use. Hypohydrophily increased with precipitation, whereas monoecious aquatic plants increased in lakes surrounded by urbanized area. The relative ratio of floating to submerged plants has increased over time. Our results provide insight into long-term changes in aquatic plant communities and identify functional traits sensitive to environmental change.

Global patterns and determinants of lake macrophyte taxonomic, functional and phylogenetic beta diversity

Authors

Jorge García-Girón, Jani Heino, Lars Baastrup-Spohr, Claudia P. Bove, John Clayton, Mary de Winton, Tõnu Feldmann, Margarita Fernández-Aláez, Frauke Eckeg, Patrick Grillas, Mark V. Hoyer, Agnieszka Kolada, Sarian Kosten, Balázs A. Lukács, Marit Mjelde, Roger P. Mormul, Laila Rhazi, Mouhssine Rhazi, Laura Sass, Jun Xu, Janne Alahuhta

Documenting the patterns of biological diversity on Earth has always been a central challenge in macroecology and biogeography. However, for the diverse group of freshwater plants, such research program is still in its infancy. Here, we examined global variation in taxonomic, functional and phylogenetic beta diversity patterns of lake macrophytes using regional data from six continents. A data set of ca. 480 lake macrophyte community observations, together with climatic, geographical and environmental variables, was compiled across 16 regions worldwide. We (a) built the very first phylogeny comprising most freshwater plant lineages; (b) exploited a wide array of functional traits that are important to macrophyte autoecology or that relate to lake ecosystem functioning; (c) assessed if different large-scale beta diversity patterns show a clear latitudinal gradient from the equator to the poles using null models; and (d) employed evolutionary and regression models to first identify the degree to which the studied functional traits show a phylogenetic signal, and then to estimate community-environment relationships at multiple spatial scales. Our results supported the notion that ecological niches evolved independently of phylogeny in macrophyte lineages worldwide. We also showed that taxonomic and phylogenetic beta diversity followed the typical global trend with higher diversity in the tropics. In addition, we were able to confirm that species, multi-trait and lineage compositions were first and foremost structured by climatic conditions at relatively broad spatial scales. Perhaps more importantly, we showed that large-scale processes along latitudinal and elevational gradients have left a strong footprint in the current diversity patterns and community-environment relationships in lake macrophytes. Overall, our results stress the need for an integrative approach to macroecology, biogeography and conservation biology, combining multiple diversity facets at different spatial scales.

Estimation of lake ecological quality from Sentinel-2 remote sensing imagery

Authors

Gary Free, Mariano Bresciani, Wayne Trodd, Deirdre Tierney, Shane O’Boyle, Caroline Plant & Jenny Deakin

The Water Framework Directive requires European states to monitor the ecological quality of their lakes. Detailed information on the composition and abundance of biological groups such as aquatic plants (macrophytes) and phytoplankton (including chlorophyll a) must be expressed as an ecological quality ratio (EQR), ranging from 1 (close to reference status) to 0 (bad status). Effort is often focused on gathering this detailed information on selected lakes at the expense of more synoptic approaches that could capture a more holistic assessment of a catchment’s water quality. This could be rectified if remote sensing can provide predictions of ecological quality for unmonitored lakes. We found that data from Sentinel-2 satellites, based on regression model outputs of observed vs estimated results, successfully predicted the macrophyte EQR (R² = 0.77) and the maximum lake depth that macrophytes colonised to (R² = 0.80) but average chlorophyll a was less well predicted (R² = 0.66). Predictions for a test catchment indicated that results were within one ecological assessment class width of measured values for macrophytes. This approach can potentially estimate status for unmonitored lakes in Ireland, be integrated with results on monitored lakes and used to direct resources where needed at national and catchment scales.

 

A new approach to the biological monitoring of freshwater systems: Mapping nutrient loading in two South African rivers, a case study

Authors

Samuel N. Motitsoe, Martin P. Hill, Trevor S. Avery, Jaclyn M. Hill

Excessive addition of nitrogen (N) has threatened aquatic ecosystems for decades. Traditional water quality and biological monitoring assessment tools are widely used for monitoring nutrient loads and ecosystem health, but most of these methods cannot distinguish between different types and sources of pollution. This is a challenge, particularly when dealing with non-point sources of anthropogenic nitrogen inputs into freshwater systems. Recent laboratory studies using stable isotopic ratios (δ¹⁵N and C/N) of aquatic macrophytes (duckweed: Spirodela spp.) have shown successful differentiation and mapping between different N-sources and further, showed abilities to act as early warning indicators for environmental N-loading. Therefore, the aim of this study was to field test the potential of stable isotopic values of transplanted Spirodela spp. to map temporal and spatial N-loading variation and determine the main sources of N-loading in two river systems in the Eastern Cape Province of South Africa, using previously grown, isotopically calibrated and transplanted Spirodela plants, collected over a 13-month sampling period. Nitrogen isotopic values (δ¹⁵N) of Spirodela plants traced environmental N-loading and identified pollution hotspots and sources through time and space over a wide range of nutrient gradients. δ¹⁵N isotopic values of Spirodela spp. provided detailed dynamics on N-loading, therefore supporting its utilisation in the biological monitoring of ecosystem health and the early detection of eutrophication in freshwater systems.

Review: Toward management of urban ponds for freshwater biodiversity

Authors

Beat Oertli, Kirsten M. Parris

Many cities around the world are expanding and this trend in urbanization is expected to sharply increase over coming decades. At the same time, the integration of green and blue spaces is widely promoted in urban development, potentially offering numerous benefits for biodiversity. This is particularly relevant for urban waterbodies, a type of ecosystem present in most cities. However, site managers often lack the knowledge base to promote biodiversity in these waterbodies, which are generally created to provide other ecosystem services. To address this, our review presents guidelines for promoting biodiversity in urban ponds. We found a total of 516 publications indexed in ISI Web of Sciences related to this topic, of which 279 were retained for the purposes of our review. The biodiversity of urban ponds, measured by species richness, appears to be generally lower than in rural ponds; however, urban ponds often support threatened species. Furthermore, if well managed, urban ponds have the potential to support a much greater biodiversity than they currently do. Indeed, this review shows that a range of urban factors can impair or promote pond biodiversity, including many that can easily be controlled by site managers. Local factors include design (surface area, pond depth, banks and margins, shade, shoreline irregularity), water quality (conductivity, nutrients, heavy metals), and hydroperiod and biotic characteristics (stands of vegetation, fish, invasive species). Important regional factors include several indicators of urbanization (roads, buildings, density of population, impervious surfaces, car traffic), and the presence of other wetlands or green spaces in the surrounding landscape. We considered each of these factors and their potential impact on freshwater biodiversity. Taking into account the management measures listed in the publications reviewed, we have proposed a framework for the management of urban ponds, with guidelines to promote biodiversity and other ecosystem services, and to avoid ecosystem disservices or the creation of ecological traps. At the city scale, the biodiversity of a pondscape benefits from a high diversity of pond types, differing in their environmental characteristics and management.

Cyanobacteria in small water bodies: The effect of habitat and catchment area conditions

Authors

Anna Kozak, Sofia Celewicz-Gołdyn, Natalia Kuczyńska-Kippen

Cyanobacteria are an important component of microalgae communities in aquatic ecosystems, however, their response to environmental factors in different habitats and catchment areas of small water bodies is still not well recognised. We examined ponds from two types of surroundings (field vs. forest) in order to find the best triggers for the distribution of cyanobacteria species, and analysed different habitats (open water and macrophyte-dominated zones) to find the habitat preferences of cyanobacteria species.

Our results underline the important role of habitats in the determination of the abundance of cyanobacteria species in small water bodies. Cyanobacteria as a group preferred macrophyte-dominated sites with stable water column conditions, which to lesser extent were inhabited by representatives of other systematic groups of algae. The co-occurrence of many cyanobacteria species and zooplankton in the studied ponds may have indirectly resulted from biotic interactions in the food web. In the open water a positive relationship between zooplankton and cyanobacteria suggests stimulation of their development through the elimination of smaller edible taxa or by nutrient resupply through zooplankton excretion.

The type of catchment area also impacted the cyanobacterial community. Field ponds with significantly higher values of pH and NO₃ were characterised by a higher abundance of cyanobacteria compared with ponds within the forest catchment. A positive relationship between pH and cyanobacteria indicates that they raise pH during photosynthesis. However, some species were negatively associated with water temperature and occurred exclusively only in forest ponds.

The study revealed that cyanobacteria in small water bodies can be a valuable indicator of important ecosystem conditions. Despite the fact that their prevalence in agricultural ponds may confirm their potential as an indicator of pollution, their high diversity associated with macrophytes contributes to an increase of overall landscape biodiversity.

Photodegradation of algae and macrophyte-derived dissolved organic matter: a multi-method assessment of DOM transformation

Authors

Shasha Liu, Weiying Feng, Fanhao Song, Tingting Li, Wenjing Guo, BeiBei Wang, Hongyang Wang, Fengchang Wu

Due to the frequent occurrence of algal bloom and eutrophication, algae and macrophyte-derived dissolved organic matter (DOM) play a more important role in the lake environment. In the study, algae and macrophyte-derived DOM were exposed for 30 days either in the dark or light in order to develop a broader understanding of their photochemical and microbial transformation. Changes of quantification and quality of DOM were characterized by Uv-visible spectroscopy, fluorescence spectroscopy, Fourier infrared spectroscopy, and nuclear magnetic resonance spectroscopy. Simulated solar UV exposure (30 d) without sterilization removed 49.7% and 42.4% of the dissolved organic carbon (DOC) from chlorella and water chestnut DOM, respectively. In contrast, 31.6% and 22.2% of DOC were removed under dark conditions accordingly. Compared with humic OM, autochthonous DOM was more biolabile and less photolabile, with less photochemical removal of DOC in this study. Molecular structures of studied DOM exhibited selective alterations during incubation. Fluorescence spectroscopy revealed that fulvic acid-like substances were susceptible to photodegradation, while protein-like substances were susceptible to both photodegradation and biodegradation. Furthermore, analytic results of carbon functional groups suggested that polysaccharides were more biolabile; aromatics were more photolabile; and phenols/aromatic proteins were both biolabile and photolabile. The higher proportion of aliphatics and lower proportion of aromatics in autochthonous DOM might be the primary cause of their greater biodegradation and weaker photodegradation.

Do benthic algae provide important information over and above that provided by macrophytes and phytoplankton in lake status assessment? – Results from a case study in Norway

Authors

Susanne C. Schneider, Dag Hjermann, Hanne Edvardsen

To test if phytobenthic algae provide additional important information to macrophytes and phytoplankton for lake monitoring, we sampled two large lakes in Norway. In each lake, we analyzed water chemistry and phytoplankton above the deepest site, recorded macrophytes and non-diatom phytobenthic algae at 20 sites around the shoreline and estimated site-specific nutrient input from land cover. Since no ready-to-use phytobenthos index exists for lakes in Norway, we tested the PIT index developed for rivers, commonly perceived signs of disturbance such as high algal cover, and taxon richness as well as similarity patterns. Both lakes were nutrient poor, but had potential local nutrient inputs (villages, agriculture). In neither of the lakes did phytobenthos indicate a worse overall ecological status than macrophytes and phytoplankton. Our data therefore, did not suggest that it would be useful to add phytobenthos into surveillance monitoring of lakes in Norway. There was a loose correlation between macrophyte and phytobenthic site-specific taxon richness and similarities. This means that macrophytes and phytobenthos do indeed give partly redundant information. High algal cover was found at sites with both high and low phosphorus input. Using algal cover as indicator of site-specific nutrient input is therefore overly simplistic. Urban and cultivated areas were associated with a more eutrophic PIT. This indicates that the PIT, despite being developed for lotic waters, may be used to detect site specific nutrient input in lakes.

The transformation of macrophyte‐derived organic matter to methane relates to plant water and nutrient contents

Authors

Charlotte Grasset, Gwenaël Abril, Raquel Mendonça, Fabio Roland, Sebastian Sobek

Macrophyte detritus is one of the main sources of organic carbon (OC) in inland waters, and it is potentially available for methane (CH₄) production in anoxic bottom waters and sediments. However, the transformation of macrophyte‐derived OC into CH₄ has not been studied systematically, thus its extent and relationship with macrophyte characteristics remains uncertain. We performed decomposition experiments of macrophyte detritus from 10 different species at anoxic conditions, in presence and absence of a freshwater sediment, in order to relate the extent and rate of CH₄production to the detritus water content, C/N and C/P ratios. A significant fraction of the macrophyte OC was transformed to CH₄ (mean = 7.9%; range = 0–15.0%) during the 59‐d incubation, and the mean total C loss to CO₂ and CH₄ was 17.3% (range = 1.3–32.7%). The transformation efficiency of macrophyte OC to CH₄ was significantly and positively related to the macrophyte water content, and negatively to its C/N and C/P ratios. The presence of sediment increased the transformation efficiency to CH₄ from an average of 4.0% (without sediment) to 11.8%, possibly due to physicochemical conditions favorable for CH₄ production (low redox potential, buffered pH) or because sediment particles facilitate biofilm formation. The relationship between macrophyte characteristics and CH₄ production can be used by future studies to model CH₄ emission in systems colonized by macrophytes. Furthermore, this study highlights that the extent to which macrophyte detritus is mixed with sediment also affects CH₄ production.