East Taihu Lake Research Articles

Corrigendum to “Changes in aquatic vegetation communities based on satellite images before and after pen aquaculture removal in East Lake Taihu”

由于作者的疏忽和编辑把关不严，杨井志成, 罗菊花, 陆莉蓉等发表在《湖泊科学》2021年第2期507-717页的论文“东太湖围网拆除前后水生植被群落遥感监测及变化“（DOI: 10.18307/2021.0228）中的前言部分述及的浮游藻类指数(floating algae index, FAI)和后文提出的藻类指数(FAI)使用了同一个缩略语FAI表述，容易造成读者误解. 由于FAI在相关文献中已经广泛使用，本文提出的藻类指数应该改为AI (Algae Index, AI), 对应的1.4节所有段落、表2、图2等部分的FAI均应该是AI. 此外，图3中的上部两幅假彩色遥感图的图例加注为排版错误，不应加注图例，应删除. 特此勘误.;The corrigendum is for the following paper published by Yang Jingzhicheng et al “Changes in aquatic vegetation communities based on satellite images before and after pen aquaculture removal in East Lake Taihu” (J. Lake Sci.2021,33(2):507-517. DOI:10.18307/2021.0228). Due to the carelessness of the authors and the editor, the FAI for algae index in Chpt. 1.4, Fig.2 and Tab.2 is misused, which should be presented as algae index (AI). The FAI was a common abbreviation for floating algae index as indicated in Preface and references, such a misuse could lead a misunderstanding for the readers. In addition, the legends on the upper two figures in Fig.3 are redundant, which is a casual mistake during proof-reading and should be deleted. We regret for the inconvenience to the readers.

Changes of water exchange cycle in Lake Taihu (1986-2018) and its effect on the spatial pattern of water quality

针对太湖水体交换周期近十余年发生的变化，本文收集整理了1986—2018年太湖水文巡测、汛期水文巡测数据以及太湖流域沿江城市引水量、流域降雨量变化数据，基于太湖出入湖水量的变化研究了太湖水体交换周期的变化及原因，并对交换周期变化对水质空间格局的影响进行分析.结果表明：太湖入湖水量有显著上升，2007年以来平均每年入湖水量增长30.8亿m³/a.水体交换周期显著下降，2007年以后约为184 d，相比2007年前下降了26 d.太湖流域及各水利分区近70年来，除去2015和2016年，降雨量无显著变化，主要入湖区下垫面变化造成的入湖水量增加估算在每年2.0 m³左右.太湖入湖水量增加主要集中在湖西区，与沿江口门引水量明显相关.相比2007年前，沿江口门引水量年均增长28.9亿m³/a，而这期间太湖入湖水量增量与这一引水有关.入湖水量的增加开始影响太湖存在的“西浊东清”水质结构，水体交换周期缩短会使东西太湖水质出现均化的现象，东部太湖水质会出现下降的趋势.;In view of the changes of Lake Taihu water exchange cycle in recent ten years, this paper collected and sorted out the hydrological survey data of Lake Taihu from 1986 to 2018, the water diversion quantity change of cities along the Yangtze River in Taihu Basin, rainfall change data of the basin, studied the changes and reasons of Lake Taihu water exchange cycle based on the changes of water inflow and outflow in Lake Taihu, and analyzed the effect of the change of water exchange cycle on water quality spatial pattern. The results show that the inflow of Lake Taihu has increased significantly, with an average annual inflow of 3.08 billion m³/a from 2007. The water exchange cycle has dropped significantly. It is about 184 days after 2007, which is 26 days lower than that before 2007. Over the past 70 years in the Taihu Basin and various water conservancy divisions, except for 2015 and 2016, there has been no significant change in rainfall. The increase in the amount of water inflow into Lake Taihu caused by changes in the underlying surface of the main lake inflow area is estimated to be about 2.0 m³/a. The increase of water inflow into Lake Taihu is mainly concentrated in the west of Lake Taihu, which is obviously related to the water diversion along the Yangtze River. Compared with that before 2007, the water diversion volume along the Yangtze River has increased by 2.89 billion m³ on annual average, and the increase in the amount of water inflow into Lake Taihu during this period is related to this diversion. The increase of water inflow into Lake Taihu began to affect the water quality structure of “Turbid in the West and Clear in the East”. The shortening of the water exchange cycle will homogenize the water quality of east and west Lake Taihu, and the water quality of the east Lake Taihu will show a downward trend.

Effects of environmental change on subfossil Cladocera in the subtropical shallow freshwater East Taihu Lake, China

East Taihu Lake (the south-eastern portion of Taihu Lake in China) suffers from eutrophication. The study of lacustrine subfossil zooplankton assemblages can be used to reconstruct the long-term evolution of lake water environments. In particular, the analysis of subfossil Cladocera can indicate historical changes in aquaticplants, water level, trophic states, and human disturbance in lakes. In this study, we correlated downcores changes in cladoceran assemblages with several geochemical proxies to identify the response of Cladocera to environmental change in East Taihu Lake over the past one hundred years. Redundancy analysis (RDA) and Pearson correlation analysis identified significant correlations between total phosphorus (TP) and Bosmina spp. (total), B. (E.) longispina, and Chydorus cf. sphaericus (correlation coefficients: −0.720 (P < 0.01), −0.646, and 0.667 (P < 0.05), respectively). We observed decreasing abundances of subfossil Bosminidae and increases in littoral cladoceran species and TP after the 1960s, coinciding with the introduction of land reclamation for fish and crab farming. These anthropogenic pressures exacerbated eutrophication, which led to the rapid growth of submerged vegetation and subsequently altered the zooplankton assemblage.

Phytoplankton functional groups succession and their driving factors in a shallow subtropical lake

The succession of phytoplankton functional groups and environmental variables were investigated from January to December 2018 in a shallow subtropical lake, East Taihu Lake, located in the Yangtze Delta of China. Altogether, 125 genera, 21 functional groups, and 7 predominant functional groups, D (Fragilaria acus, Synedra acus, and Nitzschia spp.), P (Fragilaria capucina and Aulacoseira granulate), MP (Oscillatoria spp., Diploneis ovalis, Gomphonema angustatum, Nitzschia palea, and Achnanthes spp.), Y (Cryptomonas ovata, Cryptomonas erosa, Chroomonas acuta, and Ceratium spp.), H2 (Anabaena spp.), M (Microcystis spp.), and W1 (Euglenoids spp.), were identified, and these predominant functional groups exhibited strong seasonal variations. Groups Y and W1 dominated from winter to spring when temperature and light were low. The external pollution load and high levels of nutrients entered the lake in June, allowing group M to become dominant, even ultimately triggering Microcystis blooming. Meanwhile, the abundance of aquatic plants in summer, combined with high levels of transparency and light availability, resulted in Group M being replaced by Group P and then Groups M and H2 rebounding in autumn. The redundancy analysis revealed that water temperature, nutrients, and light availability (Zeu/Zmix) were the key factors promoting phytoplankton succession. The ecological assessment results demonstrated a good ecological status based on the assemblage index (Q average = 3.0). This work emphasizes the fact that temperature, nutrients, and light were the driving factors for phytoplankton dynamics, and aquatic plants and external pollution were important external factors for the succession of phytoplankton.

Formation of odorous by-products during chlorination of major amino acids in East Taihu Lake: Impacts of UV, UV/PS and UV/H2O2 pre-treatments

Certain amino acids (AAs) can form odorous aldehydes, nitriles and N-chloroaldimines during chlorination. Ultraviolet (UV) photolysis, ultraviolet/persulfate (UV/PS) and ultraviolet/hydrogen peroxide (UV/H2O2) treatments have been reported to decrease trace organic contaminants in drinking water. In this study, 20 common AAs in East Taihu (ET) Lake (the main drinking water source for the surrounding cities) were determined during one year (four seasons). The impacts of UV photolysis alone and two UV-advanced oxidation process (AOP) pre-treatments on the formation of aldehydes, nitriles and N-chloroaldimines during post-chlorination of water containing three of the most detected AAs (i.e. valine (Val), leucine (Leu) and isoleucine (Ile)) in ET Lake were investigated. Results showed that the two UV-AOPs significantly decreased the odorous by-product formation from AAs compared with UV photolysis alone. The formation of N-chloroaldimines was more easily controlled than that of aldehyde and nitrile. Furthermore, UV/H2O2 was more effective than UV/PS at pH = 5 and 7. At pH = 9, the two UV-AOPs had similar effects and did not perform very well. In addition, the UV-AOPs controlled the formation of odorous by-products effectively at Cl/AA (molar ratio of chlorine to amino acid) ratios of 2.4 and 3.0 but increased their formation at Cl/AA ratios of 0.8 and 1.2. Experiments in real water showed that UV/H2O2 was more suitable for controlling the off-flavor problem caused by chlorination of AAs in ET Lake.

Distribution of epipelic algae and related environmental nutrients in Taihu Lake, revealed by HPLC analysis

Epipelic algal biomass and composition (determined by HPLC pigment analysis) and related environmental nutrients were investigated in a phytoplankton-dominated area (Meiliang Bay), a macrophyte-dominated area (East Taihu Lake) and a transition zones (Gonghu Bay) in a shallow eutrophic freshwater lake (Taihu Lake, eastern China). Surface sediment samples were collected at 11 sampling sites in April and August 2016. Average epipelic algal biomass for Meiliang Bay, Gonghu Bay and East Taihu Lake was 6.5, 4.9 and 4.6μg chlorophyll (Chl)-ag–1 sediment respectively in April, and 3.8, 7.4 and 2.7μg Chl-ag–1 sediment respectively in August. The maximum biomass of epipelic algae appeared at the G1 sampling site (9.6μg Chl-ag–1 sediment) in August, whereas the minimum biomass of epipelic algae appeared at the E4 sampling site (1.7μg Chl-ag–1 sediment). Pigment (fucoxanthin, zeaxanthin and Chl-b) to Chl-a ratios indicated that epipelic algae were primarily diatoms, secondarily cyanobacteria and lastly green algae in Taihu Lake. Epipelic algae were significantly correlated with total nitrogen in the water and total phosphorus in the sediment (P&amp;lt;0.05), except for green algae. In general, using pigment as an indicator revealed that the epiphytic algal community varied over time and space. The distribution of variations in epipelic algae was related to the heterogeneity of environmental factors.

Remedial function of submersed macrophyte &lt;i&gt;Vallisneria natans&lt;/i&gt; to PAHs-contaminated sediments

沉水植物是浅水湖泊生态系统的关键种群，对水环境质量及水生生态系统结构有重要影响.以东太湖大水港和湖湾区2个典型的具有不同污染程度的沉水植物苦草（Vallisneria natans）生长区域为研究对象，考察苦草对多环芳烃（PAHs）的修复效果.结果表明，经过34 d植物修复试验，重度污染的东太湖大水港沉积物中PAHs的去除率为62%，沉积物中PAHs降解速率为0.024 d^-1；而中度污染的东太湖湖湾区沉积物的PAHs去除率为42%，其降解速率为0.015 d^-1.种植苦草的沉积物中PAHs的降解速率是未种植苦草的降解速率的2~3倍.苦草对沉积物中高分子量PAHs的修复效果尤为显著.因此，苦草可以有效地用于PAHs污染沉积物的修复，尤其是在重污染和高分子量PAHs污染沉积物中，苦草的修复作用更加明显.;Submersed macrophytes are an important functional and structural element of shallow aquatic ecosystems. Remedial function of submersed macrophyte (Vallisneria natans) to PAHs in freshwater sediments was investigated in different pollution levels in east Lake Taihu. Over a 34-day plant remediation experiment, the removal rate and the first-order rate constants of PAHs degradation in the heavily contaminated sediments of Dashui harbour from east Lake Taihu was 62% and 0.024 d^-1, respectively. However, 42% PAHs removal and 0.015 d^-1 of PAHs degradation rate was also observed in the moderately contaminated sediments of east Lake Taihu bay. The degradation rate of PAHs in the planted sediments was 2-3 times higher than those in the unplanted sediments. The removal of high molecular weight (HMW) PAHs in sediments with planting V. natans was significantly observed. Thus, V. natans can be effectively used for the remediation of PAHs contaminated sediments, especially in heavily polluted and HMW-PAHs contaminated sediments.

Changes of water temperature and heat flux at water-sediment interface, East Lake Taihu

Changes of water temperature and heat flux at water-sediment interface, East Lake Taihu

CO2 alters community composition of freshwater phytoplankton: A microcosm experiment

The effects of CO2 and related changes in water carbonate chemistry on freshwater phytoplankton were studied in in situ microcosm experiments, performed in East Lake Taihu, in August 2013 and April 2014, respectively. The microcosm treatments represented low (270ppm), present (380ppm), and high (750ppm) pCO2 conditions. Elevated CO2 decreased pH and increased aqueous CO2 concentrations, and did not change alkalinity. The maximum reduction of pH was 0.26 when CO2 increased from current level to 750ppm at the ending of experiment in the spring. The rise of pCO2 stimulated the growth of phytoplankton, and the net primary production could increase by 35% when CO2 was elevated from current level to 750ppm in summer. Interestingly, our results indicated that increasing pCO2 affected phytoplankton community structure in the microcosms. Cyanobacteria tended to be superior under high pCO2, with two species Anabaena circinalis and Anabaena eucompacta benefitting from the rising pCO2. The response of chlorophytes and diatoms to the rise of pCO2 depended on taxa. In contrast, increased CO2 did not change biomass or productivity of phytoplankton in spring, when biomass was relatively low.

Spatial distribution and bioaccumulation of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) in snails (Bellamya aeruginosa) and sediments from Taihu Lake area, China

Taihu Lake area is one of the densest metropolitan areas in the world including diverse industrial activity. In the present study, the snail (Bellamya aeruginosa) and sediment were collected from the Taihu Lake area to investigate the contamination status, congener pattern, spatial distribution, and bioaccumulation effect of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs). The samples underwent liquid extraction, lipid removal by sulfuric acid, and acidic silica gel column, and subsequently analyzed by gas chromatography-electron capture detector (GC-ECD) and gas chromatography-mass spectrometry (GC-MS). Concentration of ∑22PCBs ranged between 90 and 680 ng g−1 lipid weight in the snails and between 0.018 and 0.82 ng g−1 dry weight in the sediments. Concentration of ∑24PBDEs varied from 25 to 200 ng g−1 lipid weight in the snails and from 0.62 to 67 ng g−1 dry weight in the sediments. The levels of PCBs and PBDEs observed were in the medium to low range compared with other studies in the world. CB-153 was the predominant PCB congener in both snails and sediments whereas BDE-209 showed a low bioavailability in the snails, even if it contributed up to 70% of ∑24PBDEs in the sediments. The spatial distribution showed that the highest concentration of PCBs and PBDEs were detected in samples from Zhushan Lake. East Taihu Lake and Dianshan Lake showed lower concentration of PCBs and PBDEs than the other sampling sites. Biota-sediment accumulation was found between snails and sediments of most of PCB and PBDE congeners except for the highly brominated BDEs (i.e., BDE-209). Therefore, sediment is suggested to be an appropriate matrix to monitor BDE-209 while aquatic species such as the snail could be good for monitoring of PCBs and lower brominated BDE congeners. No significant correlation (Spearman correlation test, two-tailed) of CB-153 (r = 0.54, p = 0.27) or BDE-47 (r = 0.60, p = 0.21) was found between snails and sediments.

Long-Term Study of the Relationship between Precipitation and Aquatic Vegetation Succession in East Taihu Lake, China.

Based on long-term rainfall measurements (1956–2012), water level records (1956–2006), and aquatic plants field survey data (1960–2014), the relationship between precipitation and aquatic vegetation succession in east Taihu Lake, China, is studied. Neither abrupt changes nor any trends were found in the annual rainfall series in Taihu Lake during the studied period (1956–2012). However, for seasonal variations, statistically significant decreases are found in spring and autumn, while the rainfall in winter exhibits statistically significant increase. No significant trend was obtained in summer. A “dry” period was detected in our studied period (1963/1964~1978/1979). Total annual rainfall was significantly positively correlated to the number of rain-days (r = 0.59) and the water level (r = 0.84). Our results indicate that the variations of rainfall and water level may have an impact on the aquatic plants in Taihu Lake. The dry period may be not suitable for the growth of the aquatic plants. All aquatic plants in Taihu Lake were dramatically reduced in the dry period, especially for submerged macrophytes and floating-leaf macrophytes. Our results may be helpful for the aquatic restoration in the future.

Insight into the spatial distribution of nutrient elements and sediments fraction analysis in Taihu Lake

Lake eutrophication in China is a serious issue and has raised urgent attention, which is required for a better understanding of the eutrophic status. Particularly, the eutrophication of shallow lakes has received public attention for shallow lakes are vulnerable to changes in eutrophic status due to the closer proximity with bottom lake sediments. Herein, a comprehensive investigation on the spatial distribution of nutrient elements (including carbon, nitrogen and phosphorus) was conducted in a typical large shallow lake Taihu Lake, and the internal patterns between the distribution and eutrophic status were analyzed. The results showed that the distributions of nutrient elements in surface sediment displayed spatial diversity in different regions. Zhushan Bay, East Taihu Lake and Dongjiaozui Bay hold distinguished pattern of nutrient contents due to the different geographical locations and economic pattern of adjacent areas. Specifically, the concentrations of total carbon and total nitrogen in East Taihu Lake were significantly higher than other areas, and total phosphorus content in Zhushan Bay was the highest. Furthermore, different phosphorus fractions in sediment and eutrophic indicators of water column were further analyzed to reveal the potential contribution of sediments to nutrient loadings of overlying water. The phosphorus fraction analysis suggested that calcium bounded phosphorus accounted for the main component. Correlation analysis revealed the internal relations among various characteristics in sediment or water, which indicated that microcystis blooms were accompany with excessive COD and phosphorus and depletion of dissolved oxygen. The results offered a comprehensive understanding of the lake eutrophic status and benefited further the study on the ecological status assessment.

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 (Zeu) 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 (Zeu/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 Zeu/WD. A significant relationship was observed between Zeu/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 Zeu/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 Zeu/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 Zeu/WD was further obtained using MODIS satellite-derived Zeu 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.

Relative contribution of iron reduction to sediments organic matter mineralization in contrasting habitats of a shallow eutrophic freshwater lake

Iron reduction is one of the important organic matter (OM) mineralization pathway in sediments. Here we investigated the rates and the relative contribution of iron reduction to OM mineralization in Zhushan bay (ZSB, cyanobacterial bloom biomass (CBB)-dominated habitats) and East Taihu Lake (ETL, submerged macrophypes (SM)-dominated habitats) of Lake Taihu, China. Anaerobic microcosm incubation revealed that the rate of iron reduction at ZSB (4.42 μmol cm−3 d−1) in summer was almost 1.5 times higher than at ETL (3.13 μmol cm−3 d−1). Iron reduction accounted for 66.5% (ZSB) and 31.8% (ETL) of total anaerobic carbon mineralization, respectively. No detectable methanogenesis was found at ZSB, while methanogenesis was responsible for 16.7% of total anaerobic respiration in sediments of ETL. Geochemical analysis of solid phase constituents indicated that ZSB surface sediments experienced highly oxidizing conditions with much higher amorphous Fe(III) (71 mmol m−2) than ETL (11 mmol m−2). Conversely, AVS inventories at ETL (38 mmol m−2) were up to 30 times higher than at ZSB (1.27 mmol m−2), indicating significant sulfate reduction in sediments of ETL. Overall results suggested that varying carbon sources and distinct geochemical characterizations of the sediments in contrasting habitats significantly influenced the rate of iron reduction and the pathway of C mineralization in a large freshwater lake.

Erratum to: Ontogenetic changes in isotopic signatures of an omnivorous fish Cultrichthys erythropterus in East Lake Taihu, China

The relationship between body size and stable isotopic signatures of the omnivorous Redfin Culter (Cultrichthys erythropterus), commonly found in East Lake Taihu, was investigated. Previous analyses of C. erythropterus stomach contents have shown that this species undergoes a diet switch from being predominantly zooplanktivorous to piscivorous during its life history. This was confirmed by stable carbon isotopic signature (δ13C) in this study, in which δ13C was positively correlated with both standard length and weight. The importance of littoral-benthic resources in supporting C. erythropterus during its lifespan was also demonstrated using a two-source mixing model, the results of which showed a significant increasing trend in the contribution of littoral-benthic energy. However, the stable nitrogen isotopic signature (δ15N) exhibited an unusual pattern compared with previous studies. The δ15N of C. erythropterus showed no relationship with body size, even though dietary changes were observed. This indicated that δ15N alone cannot fully reflect a diet shift in a species and possible variability in isotopic signatures over its life history. This should be considered when using stable isotopic signatures to investigate intra-specific variations and the timing of life-history events, such as estimating the trophic positions of fish species.

Benthic Bacteria Community Changes in Responses to Different Organic Resources from Macrophyte- and Algae-Dominated Areas of Lake Taihu, China

Carbon resources play an important role in affecting the benthic bacterial community in shallow lakes. In this study, pyrosequencing was applied to compare bacteria phylogenic profile in incubated sediments with normal and exchanged organic detritus in macrophyte-dominated East Lake Taihu and algal-dominated Meiliang Bay. We observed significant bacteria species variations in sediments from two bays, regardless of treatments. RDA (Redundancy Analysis) analysis showed that sediment characteristics, especially concentrations of total nitrogen might account for this differentiation. Besides, algal-dominated Meiliang Bay sediment with addition of Vallisneria detritus exhibited higher bacterial species variations than the sediment amended with Microcystis detritus. To the contrary, sediments from macrophyte-dominated East Lake Taihu shared similar bacteria profile at all taxonomic levels and grouped together in MDS (multidimensional scaling) plots over the treatments with Vallisneria or Microcystis detritus addition into the sediment. We speculated that the different degradability of macrophyte detritus and algal detritus led to varied bacterial responses to exchanged organic resources and ultimately, the amounts, nutrient availability and degradability of organic resources may be main reasons for benthic bacteria community structure differentiation between the two states in shallow lakes.

Antioxidant Responses of Vallisneria asiatica to Eutrophic Sediments in Lake Taihu, China.

Three kinds of representative sediments were obtained from a macrophyte-dominated bay (East Lake Taihu) and two algae-dominated regions (Western Lake Taihu and Meiliang Bay). Physiological responses of Vallisneria asiatica to these sediments were compared. Results from 20 days exposures showed no obvious differences in malondialdehyde (MDA) in roots, while the MDA content in leaves of plants exposed to Western Lake Taihu sediment was significantly (p<0.05) higher than those exposed to the other two sediments. In comparison to the other two sediments, plants exposed to Western Lake Taihu sediment showed significantly lower (p<0.05) superoxide dismutase in roots and leaves on the 10th and 40th day. On the 40th day, root catalase (CAT) activities in V. asiatica from Western Lake Taihu and Meiliang Bay sediments were lower than that from East Lake Taihu sediment, while leaf CAT activity in V. asiatica from Western Lake Taihu sediment was higher than that from East Lake Taihu sediment (p<0.05). Western Lake Taihu sediment caused more serious oxidative stress in V. asiatica than East Lake Taihu sediment. Results indicated eutrophic sediment was a contributing factor in the disappearance of V. asiatica in Western Lake Taihu.

Long-term remote monitoring of total suspended matter concentration in Lake Taihu using 250 m MODIS-Aqua data

We have developed and validated a robust empirical model for estimating the concentrations of total suspended matter (TSM) in Lake Taihu (China), a large turbid inland water body. This model was generated using Moderate Resolution Imaging Spectroradiometer (MODIS-Aqua) medium-resolution (250m) data gathered from 2003 to 2013 and in situ data collected from a number of cruise surveys. A strong significant correlate relationship between the in situ TSM data and the atmospherically corrected MODIS-Aqua remote sensing reflectance at the 645nm band (Rrs(645)) was found (R2=0.70, p<0.001, n=150). From these data, a local TSM model was developed for Lake Taihu. Long-term TSM distribution maps retrieved from the MODIS-Aqua data demonstrated marked temporal and spatial variations. Temporally, significant lower TSM was found in summer and autumn than in winter and spring (p<0.005, t-test). The significant seasonal variability could be attributed to sediment resuspension due to changes in the wind speed between different seasons. Lake Taihu also experiences large inter-annual variations that are primarily caused by changes in wind force over the region. In particular, the TSM in Lake Taihu from 2006 to 2008 was relatively lower than in other years, which could be explained by the lower mean wind speed during these years compared to the other years. Spatially, the TSM in the Open area, especially in the southern part of this region, was consistently higher than in other sub-regions of Lake Taihu. The coverage of submerged aquatic vegetation (SAV) generally characterized East Lake Taihu as a region with a relatively lower TSM. Lake topographic conditions, SAV, and runoff discharge jointly contributed to the spatial variations in TSM.

Validating and Mapping Surface Water Temperatures in Lake Taihu: Results From MODIS Land Surface Temperature Products

Data from four in situ high-frequency monitoring sites in Lake Taihu, China were used to 1) assess the accuracy of MODIS land surface temperature (LST) products; 2) characterize the spatial and temporal variability in lake surface water temperature (LSWT) with Aqua MODIS thermal-infrared imagery; and 3) explore the causes of these variations. The validation showed that MODIS-derived LSWTs and in situ water temperatures were significantly correlated, with a coefficient of determination higher than 0.96 and a root mean square error between 1.2°C and 1.8°C. These results indicate MODIS LST products can be used to assess the spatial and temporal thermal behavior of Lake Taihu. A spatial analysis of daytime LSWT showed different thermal zones along the lake due to the differential heat storage capacity between the deep and shallow regions of the lake, such as the littoral and East Lake Taihu. In contrast, the nighttime LSWT showed little variation, and there was a uniform surface water temperature. Following a change in solar radiation, the annual cycle of the average LSWT (with a nearly 24°C range) started to increase in January and peaked in July. In Lake Taihu, the mean nighttime LSWT from July to September rapidly warmed over the period of 2002-2013 at an average rate of 0.059 ± 0.053°C/year. Our study promotes the use of MODIS LST products in limnology through a validation using a large amount of real-time synchronous water temperature data based on high-frequency observations, which were seldom used in previous studies.

Characteristics and influence to overlying water of amino acids from typical plants distributed in Lake Taihu, China

The concentrations of total hydrolyzable amino acids( THAAs) were investigated in 8 kinds of typical plants of both East Lake Taihu and Gonghu Bay,in order to find the links and differences of composition of THAAs in the typical plants,sediments and water as well as the composition of THAAs in different typical plants of Lake Taihu. The form and composition of 15 kinds of THAAs in 18 samples were analyzed by o-phthalaldehyde pre-column derivatization-RP-HPLC. The average concentration of THAAs in typical plants of East Lake Taihu was 861. 6 ± 182. 96 μmol / g. The average concentration in typical plants of Gonghu Bay was 700. 0 ± 232. 3 μmol / g. The comparison of the concentrations of THAAs in different kinds of plants showed submerged macrophytes and floating-leaved macrophytes had the highest concentration of THAAs,followed by emerged macrophytes and terrestrial plants. The dominating amino acids were Asparagine,Glutamic acid,Arginine,Alanine and Lysine,which accounted for more than 50% of concentration of THAAs. About 30. 7%-94. 7% of the N in plants were from THAAs,which was an important source of N in plants. Meanwhile,in comparison with the composition of THAAs in sediments and water in Lake Taihu,the typical plants generally aligned with sediments but different from the water. It showed that THAAs in plant may be an important source of the THAAS in sediments.