Characteristics of a landscape water with high salinity in a coastal city of China and measures for eutrophication control

Eutrophication of landscape waters is drawing public concerns in China but few studies have been conducted on the problem associated with high water salinity as what happens at Sino-Singapore Tianjin Eco-city in Tianjin, a coastal metropolis of northern China. In order to find ways for eutrophication control, a comparative study was conducted on three landscape water bodies, namely Qingjing Lake, Jiyun River and Jiyun River Oxbow, which are under varied conditions of salinity, organic, and nutrients intrusion. The spatial and temporal variations of water quality were revealed by water sampling and analyses, and correlative relationships were obtained between water salinity and other parameters related to eutrophication. By utilizing a trophic level index (TLI), the eutrophication status of the three landscape water bodies in different seasons could further be evaluated. As a result, water temperature, as expected, showed the strongest effect on eutrophication because higher TLI together with higher Chl-a concentrations tended to occur in later spring and summer seasons, while nutrient concentration, especially TP, was also the determinative factor to the eutrophication status. Of the three water bodies, the Jiyun River Oxbow showed a salinity as high as 20 g/L or more in contrast with the other two water bodies with salinity as 4–5 g/L. Although its TP concentration was usually very low (about 0.1 mg/L), it was under a moderate eutrophication status almost in all seasons, indicating that high salinity tends to induce alga growth. Dilution of saline inflow and nutrients reduction could thus be proposed as the main measures for eutrophication control of landscape waters in the study area.     

Comparative analysis of nutrients,chlorophyll and transparency in two large shallow lakes (Lake Taihu,P.R. China and Lake Okeechobee,USA)

This article compares limnological attributes of two of the world’s largest shallow lakes—Lake Okeechobee in Florida, USA and Lake Taihu in P.R. China. Both the systems support an array of ecological and societal values including fish and wildlife habitat, public water supply, flood protection, and recreation. Both have extensive research programs, largely because of concern regarding the lakes’ frequent cyanobacterial blooms. By evaluating these systems together, we compare and contrast properties that can generally advance the understanding and management of large shallow lowland lakes. Because of shallow depth, long fetch, and unconsolidated mud sediments, water chemistry, and transparency in both the lakes are strongly influenced by resuspended sediments that affect light and nutrient conditions. In the central region of both the lakes, where depth is the greatest, evaluation of limiting factors by a trophic state index approach indicates that light most often limits phytoplankton biomass. In contrast, the more sheltered shoreline areas of both the lakes display evidence of nitrogen (N) limitation, which also has been confirmed in nutrient assays conducted in earlier studies. This N limitation most likely is a result of excessive levels of phosphorus (P) that have developed in the lakes due to high external loads over recent decades and the currently high internal P recycling. Comparisons of these lakes show that Lake Taihu has higher N than, similar total phosphorus (TP) and similar light conditions to that of Lake Okeechobee, but less chlorophyll a (CHL). The latter may be as a result of lower winter temperatures in Lake Taihu (around 5°C) compared to Lake Okeechobee (around 15°C), which could reduce phytoplankton growth and abundance through the other seasons of the year. In these systems, the important role of light, temperature, and nutrients in algal bloom dynamics must be considered, especially due to possible adverse and unintended effects that might occur with projects such as sediment removal, and in the long term, in regard to buffering lake responses to external load reduction. Handling editor: D. Hamilton     

Estimation of the long-term nutrient budget and thresholds of regime shift for a large shallow lake in China

In this study, we apply an integrated empirical and mechanism approach to estimate a comprehensive long-term (1953–2012) total nitrogen (TN) and total phosphorus (TP) loading budget for the eutrophic Lake Chaohu in China. This budget is subsequently validated, firstly, by comparing with the available measured data in several years, and secondly, by model simulations for long-term nutrient dynamics using both Vollenweider (VW) model and dynamic nonlinear (DyN) model. Results show that the estimated nutrient budget is applicable for further evaluations. Surprisingly, nutrient loading from non-point sources (85% for TN and 77% for TP on average) is higher than expectation, suggesting the importance of nutrient flux from the soil in the basin. In addition, DyN model performs relatively better than VW model, which is attributed to both the additional sediment recycling process and the parameters adjusted by the Bayesian-based Markov Chain Monte Carlo (MCMC) method. DyN model further shows that the TP loading thresholds from the clear to turbid state (631.8 ± 290.16 t y⁻¹) and from the turbid to clear state (546.0 ± 319.80 t y⁻¹) are significantly different (p < 0.01). Nevertheless, the uncertainty ranges of the thresholds are largely overlapped, which is consistent with the results that the eutrophication of Lake Chaohu is more likely to be reversible (74.12%) than hysteretic (25.53%). The ecosystem of Lake Chaohu shifted from the clear to turbid state during late 1970s. For managers, approximately two-thirds of the current TP loading must be reduced for a shift back with substantial improvement in water quality. Because in practice the reduction of loading from a non-point source is very difficult and costly, additional methods beyond nutrient reduction, such as water level regulation, should be considered for the lake restoration.     

Benthic shear stress gradient defines three mutually exclusive modes of non-biological internal nutrient loading in shallow lakes

Assessment of the importance of internal nutrient loading is essential for managing and restoring eutrophic shallow lakes. To date, studies of internal loads have tended to focus on one of two abiotic processes, either molecular diffusion or sediment/nutrient entrainment (resuspension). This study presents a new approach to determining the non-biological fluxes of nitrogen (N) and phosphorus (P) from the sediment to the water column of shallow lakes. Three mutually exclusive flux processes: (i) molecular diffusion, (ii) turbulent diffusion (eddy diffusivity) and (iii) wind-induced resuspension of N and P, were related to a gradient of benthic shear stress. A model presented here allowed the durations and magnitudes of different non-biological fluxes to be calculated over time, based on benthic shear stress. Two site-specific critical shear stress thresholds determined which of the three flux processes dominated for any benthic shear stress value. The model was calibrated for a shallow lake and the continuous flux of nutrient from the sediment to the overlying water generated by each process during that period was calculated, enabling the estimation of the relative importance of each of the three flux processes over a one-year period. Wind-induced resuspension dominated the internal nutrient flux, operating for 38% of the time and contributing 0.9 T P year⁻¹ and 10.2 T N year⁻¹ to the internal nutrient load. In contrast, molecular diffusion only contributed 0.01–0.02 T P year⁻¹ and 0.12–0.20 T N year⁻¹ to the water column, while turbulent diffusion provided up to 0.6 T P year⁻¹ and 6.2 T N year⁻¹. Our model suggests that turbulent diffusion is a neglected and potentially important process contributing to internal nutrient loading in shallow lakes, whereas molecular diffusion appears to be relatively unimportant in lakes that experience turbulence at the sediment–water interface. Handling editor: L. Naselli-Flores     

Epiphytic,littoral diatoms as bioindicators of shallow lake trophic status: Trophic Diatom Index for Lakes (TDIL) developed in Hungary

Littoral diatoms are important contributors of the primary production in shallow aquatic ecosystems and they can be used as indicators of the trophic status. The aim of the study was to develop an index to assess trophic status of Hungarian lakes as suggested by the Water Framework Directive. In spring of 2005 and 2006, epiphytic diatom samples were collected from 83 shallow lakes. Weighted average method was used to develop and test the TP model. In the developed TP model correlation between the observed and diatom inferred TP was high (r ² = 0.96, n = 67). The optimum and tolerance TP parametrics of 127 species were determined and trophic indicator and sensibility values were defined for the Trophic Diatom Index for Lakes (TDIL). The TDIL was applicable to assess the ecological status of Hungarian shallow lakes. According to the TDIL the ecological status of 4 lakes were in excellent, 25 in good, 21 in medium, 21 in tolerable and 12 in bad status. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: K. Martens     

Implications of floristic and environmental variation for carbon cycle dynamics in boreal forest ecosystems of central Canada

Abstract. Species composition, detritus, and soil data from 97 boreal forest stands along a transect in central Canada were analysed using Correspondence Analysis to determine the dominant environmental/site variables that differentiate these forest stands. Picea mariana stands were densely clustered together on the understorey DCA plot, suggesting a consistent understorey species composition (feather mosses and Ericaceae), whereas Populus tremuloides stands had the most diverse understorey species composition (ca. 30 species, mostly shrubs and herbs). Pinus banksiana stands had several characteristic species of reindeer lichens (Cladina spp.), but saplings and Pinus seedlings were rare. Although climatic variables showed large variation along the transect, the CCA results indicated that site conditions are more important in determining species composition and differentiating the stand types. Forest floor characteristics (litter and humus layer, woody debris, and drainage) appear to be among the most important site variables. Stands of Picea had significantly higher average carbon (C) densities in the combined litter and humus layer (43530 kg‐C.ha^‐1) than either Populus (25 500 kg‐C.ha^‐1) or Pinus (19 400 kg‐C.ha^‐1). The thick surface organic layer in lowland Picea stands plays an important role in regulating soil temperature and moisture, and organic‐matter decomposition, which in turn affect the ecosystem C‐dynamics. During forest succession after a stand‐replacing disturbance (e.g. fires), tree biomass and surface organic layer thickness increase in all stand types as forests recover; however, woody biomass detritus first decreases and then increases after ca. 80 yr. Soil C densities show slight decrease with ages in Populus stands, but increase in other stand types. These results indicate the complex C‐transfer processes among different components (tree biomass, detritus, forest floor, and soil) of boreal ecosystems at various stages of succession.     

Stable carbon and nitrogen isotope discrimination in soft tissues of the leatherback turtle (Dermochelys coriacea): Insights for trophic studies of marine turtles

The trophic ecology of marine vertebrates has been increasingly studied via stable isotope analysis of body tissues. However, the theoretical basis for using stable isotopes to elucidate consumer–prey relationships remains poorly validated for most taxa despite numerous studies using this technique in natural systems. In this study, we measured stable carbon and stable nitrogen diet-tissue discrimination (Δ_dt) in whole blood, red blood cells, blood plasma solutes, and skin of leatherback sea turtles (Dermochelys coriacea; N = 7) maintained in captivity for up to 424 days and fed an isotopically consistent control diet with a mean C:N ratio of 2.94:1.00 and an energetic content of 20.16 ± 0.39 kJ g^− 1 Dry Mass. We used a random-effect repeated measure model to evaluate isotopic consistency among tissue samples collected on days 276, 348, and 424. Both δ¹³C and δ¹⁵N remained consistent among sampling events in all tissues (all 95% posterior intervals for the slopes of a linear model included zero), indicating that all tissues had fully integrated diet-derived stable isotope compositions. Mean tissue-specific δ¹³C ranged from − 18.30 ± 0.16‰ (plasma solutes) to − 15.54 ± 0.14‰ (skin), whereas mean δ¹⁵N was from 10.06 ± 0.22‰ (whole blood) to 11.46 ± 0.10‰ (plasma solutes). The computed Δ_dt factors for carbon ranged from − 0.58‰ (plasma solutes) to + 2.25‰ (skin), whereas Δ_dt for nitrogen was from + 1.49 (red blood cells) to + 2.85 (plasma solutes). As the only discrimination factors available for leatherback turtles, our data will be useful for future interpretations of field-derived stable isotope data for this species. The inherent variability in Δ_dt values among individuals was low, which supports the value of these data for dietary reconstructions. However, it is important to note that tissue-specific discrimination factors for leatherbacks contrast with the widely accepted values for endothermic species (0–1‰ for C, 3–5‰ for N), and are also different from values established for hard-shelled turtles. This underscores the need for species- and tissue-specific discrimination factors before interpreting trophic studies of wild animals, including marine turtles.     

The eutrophication of shallow coastal lakes in Southwest England — understanding and recommendations for restoration,based on palaeolimnology,historical records,and the modelling of changing phosphorus loads

Palaeolimnological studies of sediments from Slapton Ley and Loe Pool, two coastal freshwater lakes in Southwest England, show that in the period since 1945, they have been eutrophicated by nutrient inputs from intensification of agriculture, but also from sewage effluent. Two simple models have been used to identify the main sources of catchment outputs, and in the case of Slapton Ley, to evaluate historical changes in land use, and their likely effect on lake trophic status.Restoration strategies may also be evaluated using the same models. They suggest that in order to reduce loads on either lake to within OECD permissible limits, not only will all sewage inputs need to be prevented, and non-phosphate detergents used, but also losses from agricultural land must be reduced. This could take the form of the keeping of fewer cattle (the main source of organic nitrogen and phosphorus in both catchments), or the zoning of the respective catchments so that steep slopes close to riparian zones are not used, as at present, for the grazing of livestock.A better option, however, would appear to be the establishment along most of the rivers draining into these lakes, of buffer strips of woodland at least 15 m wide. According to the models, this measure, along with treatment or diversion of sewage effluent, would reduce phosphorus loads upon the lakes to within acceptable limits.     

Midday depression in root respiration of <Emphasis Type="Italic">Quercus crispula</Emphasis> and <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis>: its implication for estimating carbon cycling in forest ecosystems

We observed the phenomenon of midday depression in the rate of tree root respiration. Diurnal changes in the root respiration rate of Quercus crispula and Chamaecyparis obtusa were measured under intact conditions using a closed chamber method and a soil respiration measurement system (LI-6400 with a root respiration chamber) in a forest in the foothills of Mt. Fuji. After the measurement of intact root respiration in the field, the root was excised and taken to the laboratory, and the temperature dependence on the respiration rate of the detached root was measured using an open-flow gas exchange system with an infrared gas analyzer (LI-6252). The measurement was conducted in September 2003, August and November 2005, and June 2006. Whereas the root respiration rate of both species under intact conditions increased with increasing soil and root temperatures from dawn to early morning, the respiration rate decreased around midday from 10:00 to 15:00 despite an increment of soil and root temperatures. There was no clear relationship between the intact root respiration rate and root temperature in either species, although the detached root respiration rate of both increased exponentially with the temperature. The amount of the CO₂ efflux estimated using the temperature dependence of detached root respiration tended to underestimate the actual measurement value (intact respiration rate) by 20–50% in both species. These results indicate that evaluating midday depression in root respiration would be important for a more accurate estimation of the carbon cycle or net ecosystem production in forests.     

The carbon fertilization effect over a century of anthropogenic CO2 emissions: higher intracellular CO2 and more drought resistance among invasive and native grass species contrasts with increased water use efficiency for woody plants in the US Southwest

From 1890 to 2015, anthropogenic carbon dioxide emissions have increased atmospheric CO₂ concentrations from 270 to 400 mol mol^?1. The effect of increased carbon emissions on plant growth and reproduction has been the subject of study of free‐air CO₂ enrichment (FACE) experiments. These experiments have found (i) an increase in internal CO₂ partial pressure (c_i) alongside acclimation of photosynthetic capacity, (ii) variable decreases in stomatal conductance, and (iii) that increases in yield do not increase commensurate with CO₂ concentrations. Our data set, which includes a 115‐year‐long selection of grasses collected in New Mexico since 1892, is consistent with an increased c_i as a response to historical CO₂ increase in the atmosphere, with invasive species showing the largest increase. Comparison with Palmer Drought Sensitivity Index (PDSI) for New Mexico indicates a moderate correlation with Δ¹³C (r² = 0.32, P < 0.01) before 1950, with no correlation (r² = 0.00, P = 0.91) after 1950. These results indicate that increased c_i may have conferred some drought resistance to these grasses through increased availability of CO₂ in the event of reduced stomatal conductance in response to short‐term water shortage. Comparison with C₃ trees from arid environments (Pinus longaeva and Pinus edulis in the US Southwest) as well as from wetter environments (Bromus and Poa grasses in New Mexico) suggests differing responses based on environment; arid environments in New Mexico see increased intrinsic water use efficiency (WUE) in response to historic elevated CO₂ while wetter environments see increased c_i. This study suggests that (i) the observed increases in c_i in FACE experiments are consistent with historical CO₂ increases and (ii) the CO₂ increase influences plant sensitivity to water shortage, through either increased WUE or c_i in arid and wet environments, respectively.