Changes in methane oxidation activity and methanotrophic community composition in saline alkaline soils

The soil of the former Lake Texcoco is a saline alkaline environment where anthropogenic drainage in some areas has reduced salt content and pH. Potential methane (CH₄) consumption rates were measured in three soils of the former Lake Texcoco with different electrolytic conductivity (EC) and pH, i.e. Tex-S1 a >18 years drained soil (EC 0.7 dS m^?1, pH 8.5), Tex-S2 drained for ~10 years (EC 9.0 dS m^?1, pH 10.3) and the undrained Tex-S3 (EC 84.8 dS m^?1, pH 10.3). An arable soil from Alcholoya (EC 0.7 dS m^?1, pH 6.7), located nearby Lake Texcoco was used as control. Methane oxidation in the soil Tex-S1 (lowest EC and pH) was similar to that in the arable soil from Alcholoya (32.5 and 34.7 mg CH₄ kg^?1 dry soil day^?1, respectively). Meanwhile, in soils Tex-S2 and Tex-S3, the potential CH₄ oxidation rates were only 15.0 and 12.8 mg CH₄ kg^?1 dry soil day^?1, respectively. Differences in CH₄ oxidation were also related to changes in the methane-oxidizing communities in these soils. Sequence analysis of pmoA gene showed that soils differed in the identity and number of methanotrophic phylotypes. The Alcholoya soil and Tex-S1 contained phylotypes grouped within the upland soil cluster gamma and the Jasper Ridge, California JR-2 clade. In soil Tex-S3, a phylotype related to Methylomicrobium alcaliphilum was detected.     

Distribution of marine viruses and their potential hosts in Prydz Bay and adjacent Southern Ocean,Antarctic

Viruses play a key role in all marine ecosystems, and yet little is known of their distribution in Antarctic waters, especially in bathypelagic waters (>1000 m). In this study, the abundance and distribution of viruses and their potential hosts from the surface to the bottom of Prydz Bay, Antarctic, was investigated using flow cytometry. Viruses and autotrophs were abundant in nearshore and continental shelf waters, while heterotrophic bacteria and picoeukaryotes were abundant in offshore waters. Virus and bacteria abundances generally decreased with increasing depth but increased slightly just above the seafloor. Within the water column, maximum virus numbers coincided with the maximum values of chlorophyll a (when greater than 0.1 μg l^?1), in the surface and subsurface (25 m). In the open ocean, however, virus abundance usually correlated with bacterial abundance at greater depths (50, 300 and 500 m) where the surface chlorophyll a concentration was lower than 0.1 μg l^?1. Viral abundance was correlated with the host cell abundance, and this was different in different pelagic zones (bacteria and autotrophs (i.e., chlorophyll a concentration) in the epipelagic waters, picoeukaryotes and bacteria in mesopelagic waters and bacteria in bathypelagic waters). Principle component analysis and Pearson correlation analysis indicated that there was a close relationship between virus abundance and chlorophyll a, bacteria and nutrients (NO₂ + NO₃, phosphate and silicate), and picoeukaryote abundance was mainly correlated with water depth and salinity.     

Structural and functional losses in macroalgal assemblages in a southeastern Brazilian bay over more than a decade

Changes in macroalgae assemblages over more than a decade are described for Sepetiba Bay, Brazil. Variations in macroalgae abundances and functional diversity were compared with older data to test the hypothesis that their diversity decreases following anthropogenic stress that negatively impact environmental characteristics. Four field sampling excursions were undertaken at two different sites from December/2012 to May/2014. Destructive sampling per effort used six box cores (25 × 25 cm) distributed randomly along a shallow sublittoral rocky shore. Biomass was used to quantify macroalgae assemblages identified to the species level. Multivariate analyses demonstrated decreases in total biomass at both sites as well as changes in community physiognomies. The predominant corticated algae found were classified as Ecological Status Group IIA, characteristic of sites in the process of degradation and indicating that anthropogenic stress had negatively affected the macroalgae communities as evaluated by the Ecological Evaluation Index.     

Hydrogeochemical characterization of Yercaud lake southern India: Implications on lake water chemistry through multivariate statistics

In this paper, a study on the surface and deeper waters of the Yercaud Lake, Tamil Nadu, South India, was carried out to understand the geochemistry of the lake waters and also to determine its utility for agricultural purposes. Totally, 50 surface and deep water samples were collected from Yercaud Lake. Major ion and heavy metals were measured. The data obtained were interpreted using the lake water composition. The mean concentration of physicochemical parameters and heavy metals for the surface and deep waters have the following values, pH (7.6), EC (263.4), Ca^2 +(16.3), Mg^2 +(7.4), Na⁺(19.2), K⁺(1.5), Cl^?(18.2), NO₃^?(1.5), SO₄^2 ?(1.5), HCO₃^– (97.9), Fe (1.3), Mn (0.1), Cr (0.4), Cu (0.005), Pb (0.31), Zn (0.01), Co (0.095) and Ni (0.075). The data generated reflects that the water samples are dominated by recharge process, especially due to the monsoonal rains and natural springs within the lake. The geochemical data reveals that the lake water is suitable for the agricultural purpose and the chemistry of water is mainly influenced by the weathering of bedrock, especially the charnockites bedrock. The sodium adsorption ratio and sodium percentage (%Na) values indicate that the lake water is suitable for irrigation. Dominant heavy metals in the lake waters are mainly because of the lithogenic as well as through minor anthropogenic inputs. Based on our data it is noted that proper management plans are required to monitor the pollution source in the lake, with strict policy measures.     

Adaptive strategies of desmids in two tropical monomictic lakes in southeast Brazil: do morphometric differences promote life strategies selection?

Adaptive strategies of desmids in two tropical monomictic lakes were studied in relation to morphometric differences. The study aimed at evaluating desmids' strategies during inter-annual succession patterns in two tropical lakes (Dom Helvécio and Carioca) in southeast Brazil. From monthly samples of freshwater algae collected during five consecutive years (2002–2006) from the two lakes, the desmids were classified according to size, life form, and life strategies (competitive, stress tolerant, and ruderal). Our results indicated that Lake Carioca (19º45′20″S, 42º37′12″W), a small, shallow, turbid, and mesotrophic system showed dominance of invasive/opportunistic taxa (C) and R-strategists (Staurastrum species <20 μm), whereas Lake Dom Helvécio (19º45′–19º48′45″S, 42º33′45″W), a large, deep, and clear system was dominated by ruderal (R) species (Closterium aciculare and Pleurotaenium trabecula >50 μm) and tolerant to stress (S) species (Staurastrum and Staurodesmus species >20 μm). A significant number of desmids from the lakes had low MLD (≤20 μm), low volume (<10³), and high SV^?1 ratio (>1). Consequently, C-strategist species were abundant and formed a group having great adaptive value in the lakes, with higher resilience and capacity to change composition after the turnover period. Stratification stability and atelomixis were the main driving forces to sustain high desmid biomass in these two lakes, despite the greater macrophyte richness and great water column depth at Lake Dom Helvécio and the main factor influencing richness and contribution of complex forms.     

Predominance of phytoplankton-derived dissolved and particulate organic carbon in a highly eutrophic tropical coastal embayment (Guanabara Bay,Rio de Janeiro,Brazil)

We investigate the carbon dynamics in Guanabara Bay, an eutrophic tropical coastal embayment surrounded by the megacity of Rio de Janeiro (southeast coast of Brazil). Nine sampling campaigns were conducted for dissolved, particulate and total organic carbon (DOC, POC and TOC), dissolved inorganic carbon (DIC), partial pressure of CO₂ (pCO₂), chlorophyll a (Chl a), pheo-pigments and ancillary parameters. Highest DOC, POC and Chl a concentrations were found in confined-shallow regions of the bay during the summer period with strong pCO₂ undersaturation, and DOC reached 82 mg L^?1, POC 152 mg L^?1, and Chl a 800 μg L^?1. Spatially and temporally, POC and DOC concentrations varied positively with total pigments, and negatively with DIC. Strong linear correlations between these parameters indicate that the production of TOC translates to an equivalent uptake in DIC, with 85% of the POC and about 50% of the DOC being of phytoplanktonic origin. Despite the shallow depths of the bay, surface waters were enriched in POC and DOC relative to bottom waters in periods of high thermohaline stratification. The seasonal accumulation of phytoplankton-derived TOC in the surface waters reached about 105 g C m^?2 year^?1, representing between 8 and 40% of the net primary production. The calculated turnover time of organic carbon was 117 and 34 days during winter and summer, respectively. Our results indicate that eutrophication of coastal bays in the tropics can generate large stocks of planktonic biomass and detrital organic carbon which are permanently being produced and partially degraded and buried in sediments.     

Impact of anthropogenic sources on aerosol iron solubility over the Bay of Bengal and the Arabian Sea

Ambient aerosols collected from the marine atmospheric boundary layer of the Bay of Bengal and the Arabian Sea have been studied to assess the fractional solubility of aerosol iron, defined as Fe_ws (%)?=?Fe_ws/Fe_Tot?×?100; where Fe_Tot is total aerosol iron and Fe_ws is water soluble iron. The mass concentration of Fe_Tot over the two oceanic regions is not significantly different. However, the fractional solubility is 1–2 orders of magnitude higher over the Bay of Bengal (1.4–24%) compared to that over the Arabian Sea (0.02–0.4%). The spatio-temporal variability in Fe_ws (%) is attributed to differences in the nature of the mineral dust over the two oceanic regions. The Arabian Sea receives coarse dust from desert regions; whereas transport of alluvial dust from the Indo-Gangetic Plain is a dominant source to the Bay of Bengal. The poor fractional solubility (<1%) of Fe from mineral dust, hitherto overestimated in the literature, is documented for the Arabian Sea. A significant linear relationship (P-value?<?0.001) between Fe_ws (%), Fe_Tot and nss-SO₄ ^2? over the Bay of Bengal provides evidence for the chemical processing of mineral dust. Furthermore, the role of anthropogenic sources (biomass burning and fossil-fuel combustion) in enhancing the Fe_ws (%) is discernible from the chemical composition of fine mode (PM_2.5) aerosols over the Bay of Bengal. The potential impact of these Fe-dust depositions on phytoplankton carbon fixation and surface ocean biogeochemistry is discussed.     

Biochemical Characterization of a Nitrogen-Type Phosphotransferase System Reveals that Enzyme EINtr Integrates Carbon and Nitrogen Signaling in Sinorhizobium meliloti

In Sinorhizobium meliloti, catabolite repression is influenced by a noncanonical nitrogen-type phosphotransferase system (PTS^Ntr). In this PTS^Ntr, the protein HPr is phosphorylated on histidine-22 by the enzyme EI^Ntr and the flux of phosphate through this residue onto downstream proteins leads to an increase in succinate-mediated catabolite repression (SMCR). In order to explore the molecular determinants of HPr phosphorylation by EI^Ntr, both proteins were purified and the activity of EI^Ntr was measured. Experimentally determined kinetic parameters of EI^Ntr activity were significantly slower than those determined for the carbohydrate-type EI in Escherichia coli. Enzymatic assays showed that glutamine, a signal of nitrogen availability in many Gram-negative bacteria, strongly inhibits EI^Ntr. Binding experiments using the isolated GAF domain of EI^Ntr (EI_GAF) showed that it is the domain responsible for detection of glutamine. EI^Ntr activity was not affected by α-ketoglutarate, and no binding between the EI_GAF and α-ketoglutarate could be detected. These data suggest that in S. melilloti, EI^Ntr phosphorylation of HPr is regulated by signals from both carbon metabolism (phosphoenolpyruvate) and nitrogen metabolism (glutamine).     

Natural lake level fluctuation and associated concordance with water quality and aquatic communities within small lakes of the Laurentian Great Lakes region

Long-term (~20 year) data on water level, water quality and aquatic biota from four remote research areas in the Laurentian Great Lakes region were compiled to reveal patterns of natural water-level fluctuation (WLF) and associated effects on water quality and aquatic communities. Of the 16 natural lakes (no dam impoundment and lowest possible anthropogenic disturbance) yearly amplitude in water level did not exceed 1.27 m (\( \overline {\text{x}} \) = 0.26 ± 0.15 m) and yearly average water levels did not deviate greater than 0.75 m (\( \overline {\text{x}} \) = 0.10 ± 0.11 m) from the long-term mean. Linear and waveform regression analyses revealed a significant (P ≤ 0.05) decreasing trend in water levels and a 10-year oscillation in WLFs. Similarly, linear regression analysis demonstrated a significant reduction in yearly amplitude WLF over time. Correlation analyses revealed significant correlations with water quality parameters (DOC, Ca²⁺, Conductivity, pH, SO₄ ^2?) and WLFs in Boreal Shield research areas. Of the long-term biotic information available (periphyton, macrophytes, macroinvertebrates and fish) only macroinvertebrates demonstrated a significant relationship with natural WLFs. Species richness followed a unimodal response (P = 0.002, r ² = 0.66) with richness decreasing in years when water levels were either higher or lower than the long-term mean. The novel results of this study demonstrate patterns in natural WLF and associated correlations with water quality and biota across multiple lakes within the Laurentian Great Lakes region. The results are congruent with the intermediate disturbance hypothesis and have direct implications for reservoir management and climate change modeling.     

Evaluation of growth and biomass production of Arthrospira (Spirulina) fusiformis in laboratory cultures using waters from the Ethiopian soda lakes Chitu and Shala

The cost of nutrient media is the major challenge for biomass production of Spirulina. Although much effort has been made to use enriched seawater for the cultivation of this microalga, little attention has been given to the potential of water of soda lakes. In this study, growth (μ, day^?1) and biomass production (B) of Arthrospira fusiformis cultivated using waters of the soda lakes Chitu and Shala with or without supplementation were evaluated. Comparable μ and B values were achieved in both Lake Chitu water-based media (CBM) and Lake Shala water-based media (SBM), with slightly higher values in the latter. Both CBM and SBM supplemented with the standard Spirulina medium (SM) by 25 % and 50 % supported considerably higher μ and B. The pH and salinity of the cultures showed significant variations (P?μ and B. The observed higher μ and B were probably associated with the reduction in pH and salinity of the supplemented media due to addition of bicarbonate–carbonates and dilution, and provision of the limiting nutrient nitrogen. The higher μ and B in SBM may have resulted from some of their aggregate chemical parameters, which were closer to those in the SM, and abundant PO₄-P. This seems to suggest that Lake Shala water is more conducive to Arthrospira. We contend that 25 % and 50 % supplemented Lake Shala water can be preferably used to produce Arthrospira biomass, thereby reducing the cost of nutrients by 75 % and 50 %, respectively.     

The role of Gracilaria lemaneiformis in eliminating the dissolved inorganic carbon released from calcification and respiration process of Chlamys farreri

Respiration and calcification rate were estimated to quantify the effect of Zhikong scallop Chlamys farreri on marine CO₂ system in Sanggou Bay, China. The C. farreri population in Sanggou Bay sequestered 78.06?±?5.76 g C m^?2 y^?1 for shell formation, while the CO₂ fluxes due to calcification and respiration were 53.95?±?3.98 and 71.69?±?6.51 g C m^?2 y^?1, respectively. In order to eliminate the additional CO₂ released from calcification and respiration process of C. farreri, Gracilaria lemaneiformis were introduced into the integrated system and its role was validated by in situ mesocosm methods. Eight mesocosms (1,000 L) were deployed over 42-h period and consisted of four treatments: seaweed-only, scallop-only (SP), seaweed integrated with scallop (SS), and control (C). The aqueous CO₂ concentration and partial pressure of CO₂ in SP treatments were significantly higher than the other three treatments (p?<?0.01), while there were no difference between SS treatments and C treatments (p?>?0.05). Furthermore, compared with the SP treatments, the presence of the G. lemaneiformis can keep the seawater pH stable. These findings suggest that seaweed and shellfish integrated aquaculture practice cannot only reduce dissolved inorganic carbon but also can alleviate ocean acidification.     

Big changes to a small bay: introduced species and long-term compositional shifts to the fouling community of Morro Bay (CA)

Invasive species are cited as being a threat to communities and ecosystems worldwide, yet few studies have demonstrated invader impacts at these scales. Lack of historic data makes capturing large-scale community shifts problematic. We assessed long-term changes in invertebrate composition to the fouling community of a small estuary with relatively little boat traffic and no ballast water input (Morro Bay, CA). We also compared relative invasiveness of Morro Bay to international harbors (San Francisco Bay and Los Angeles/San Diego harbors). While the proportion of introduced species has not significantly changed from historic records, introduced species now occupy 86.00 % of the primary substrate. Other community shifts include; (1) a state shift to an invasive bryozoan (Watersipora subtorquata) dominated community, (2) a decrease in Mollusc richness and, (3) substantial shifts in abundance of certain species. Compared to larger more actively used harbors, Morro Bay has proportionally fewer introduced species (12.00 %) than San Francisco Bay (50.79 %) or Los Angeles/San Diego Harbors (26.23 %). Our study documents changes to a small relatively isolated estuary with little boat traffic and no ballast water input. We discuss the potential role of invasive species and other natural and anthropogenic factors as drivers of these community wide shifts. Specifically, we discuss how reintroduction of the Southern Sea Otter (Enhydra lutris nereis), an increase in sea stars (Pisaster spp.), climate change and interaction amongst potential drivers support the patterns of shifts in the Morro Bay community.     

Shear stress and sediment resuspension in relation to submersed macrophyte biomass

We examined the impacts of macrophyte beds dominated by a canopy-forming (Myriophyllum sibiricum) and a meadow-forming (Chara canescens) species on bottom shear stress (τ) and resuspension in shallow Lake Christina, Minnesota (U.S.A.). Studies were conducted in late summer, 1998, when macrophyte biomass levels exceeded 200 g m^?2, and in early summer, 2000, when biomass was greatly reduced (<20 g m^?2) in both plant beds. The critical shear stress (τ_c) of sediments, measured experimentally in the laboratory, was low (1.4 dynes cm^?2) indicating potential for resuspension in the absence of macrophytes. During 1998, turbidity was low at the M. sibiricum and Chara station, rarely increasing when calculated bottom τ (calculated from wave theory assuming no biomass obstruction) exceeded τsub c sub, indicating that both beds reduced sediment resuspension at high biomass levels. In situτ (estimated τ), measured via gypsum sphere dissolution, did not exceed τ_c above the sediment interface in either bed during 1998. In contrast, sediment resuspension occurred in both beds during similar high winds in 2000. However, estimated τ was lower than calculated bottom τ, suggesting that at low biomass, macrophytes were having some impact on τ.     

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

Ecological applications of stable isotope data require knowledge on the isotopic turnover rate of tissues, usually described as the isotopic half-life in days (T _0.5) or the change in mass (G _0.5). Ecological studies increasingly analyse tissues collected non-destructively, such as fish fin and scales, but there is limited knowledge on their turnover rates. Determining turnover rates in situ is challenging, with ex situ approaches preferred. Correspondingly, T _0.5 and G _0.5 of the nitrogen stable isotope (δ¹⁵N) were determined for juvenile barbel Barbus barbus (5.5 ± 0.6 g starting weight) using a diet-switch experiment. δ¹⁵N data from muscle, fin and scales were taken during a 125 day post diet-switch period. Whilst isotopic equilibrium was not reached in the 125 days, the δ¹⁵N values did approach those of the new diet. The fastest turnover rates were in more metabolically active tissues, from muscle (highest) to scales (lowest). Turnover rates were relatively slow; T _0.5 was 84 (muscle) to 145 (scale) days; G _0.5 was 1.39 × body mass (muscle) to 2.0 × body mass (scales), with this potentially relating to the slow growth of the experimental fish. These turnover estimates across the different tissues emphasise the importance of estimating half-lives for focal taxa at species and tissue levels for ecological studies.     

Multiple introductions and invasion pathways for the invasive ctenophore Mnemiopsis leidyi in Eurasia

The introduction and spread of non-indigenous species (NIS) in marine ecosystems accelerated during the twentieth century owing to human activities, notably international shipping. Genetic analysis has proven useful in understanding the invasion history and dynamics of colonizing NIS and identifying their source population(s). Here we investigated sequence variation in the nuclear ribosomal Internal Transcribed Spacer region of the ctenophore Mnemiopsis leidyi, a species considered one of the most invasive globally. We surveyed four populations from the native distribution range along the Atlantic coasts of the United States and South America, as well as six populations in the introduced range from the Black, Azov, Caspian and Baltic seas. Allelic and nucleotide diversity of introduced populations were comparable to those of native populations from which they were likely drawn. Introduced populations typically exhibited lower genetic differentiation (F _ST = ?0.014?C0.421) than native populations (F _ST = 0.324?C0.688). Population genetic analyses supported the invasion of Eurasia from at least two different pathways, the first from the Gulf of Mexico (e.g., Tampa Bay) to the Black Sea and thence to the Caspian Sea, the second from the northern part of the native distribution range (e.g., Narragansett Bay) to the Baltic Sea. The relatively high genetic diversity observed in introduced populations is consistent with large inocula and/or multiple invasions, both of which are possible given ballast water transport and the extensive native distribution of the ctenophore in the Atlantic Ocean.     

Phosphorus sorption characteristics of sediment in the Simiyu and Kagera River basins: implications for phosphorus loading into Lake Victoria

As part of a larger study to assess the influence of land use on riverine and atmospheric phosphorus (P) loading to Lake Victoria, P sorption characteristics of eight composite bottom sediment samples from the Simiyu and Kagera rivers were determined using the Langmuir equation. The samples had low to medium Langmuir adsorption maxima (Γ_m), ranging from 107 to 201μg g^?1. Langmuir binding energy co-efficient (K) ranged from 60 to 181μg l^?1 and the equilibrium P concentration at zero sorption (EPC₀) from 0.1 to 2.75μg g^?1. By using Langmuir co-efficients derived from P sorption experiments and soluble reactive phosphorus (SRP) concentrations measured in rivers as well as the in-shore waters of Lake Victoria, it was possible to determine the potential release of SRP into the lake by sediment from the two catchments. For the 2000 water-year, it was estimated that about 28.65 ± 0.89 (mean ± SD) and 66 ± 6.76 tons of SRP were released into Lake Victoria by sediment deposited by the Simiyu and Kagera rivers, respectively. The implications of these results to future management of cultural eutrophication in Lake Victoria are also discussed.     

Water hyacinth,Eichhornia crassipes (Pontederiaceae), reduces benthic macroinvertebrate diversity in a protected subtropical lake in South Africa

The socio-economic impacts of the free-floating aquatic plant water hyacinth, Eichhornia crassipes (Pontederiaceae), on aquatic systems are well documented, yet the impacts on aquatic biodiversity, particularly invertebrate biodiversity, are less well understood. This study aimed to determine whether the presence of water hyacinth altered the diversity and assemblage structure of benthic macroinvertebrates in a conservation area. The benthic macroinvertebrate assemblage was sampled over 1 year at five sites under water hyacinth mats and at five sites without water hyacinth at Lake Nsezi—Nseleni River in the vicinity of Richards Bay, KwaZulu-Natal, South Africa. Artificial substrates were placed beneath water hyacinth mats or in the open water to allow for colonization by freshwater macroinvertebrates, and left for a period of 6 weeks, repeated on seven occasions. Twenty nine families comprising 18,797 individuals were collected, 817 (13 families) individuals were from under water hyacinth mat sites compared to 17,980 (27 families) individuals from open water sites. Ninety-eight percent of individuals collected were, however, the invasive snail, Tarebia granifera. Open water samples were separated from samples beneath the water hyacinth mat by non-metric Multidimensional Scaling, indicating reduced biodiversity associated with the presence of water hyacinth. Exclusion of the dominant Thiaridae from the analysis did not alter the groupings. Family richness(s) and abundance (N) were significantly higher in open water communities(S: H₃ = 21.09; P = 0.0001; N: H₃ = 22.58; P = 0.00001), while evenness (J’) was higher under water hyacinth mats (H₃ = 20.13; P = 0.0002). The presence of water hyacinth had a significantly negative impact on aquatic macroinvertebrate biodiversity in a conservation area, and therefore the control of this invasive aquatic plant must play a major role in catchment management.     

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.     

Survival and movement patterns of central California coast native steelhead trout (Oncorhynchus mykiss) in the Napa River

Drawing on acoustic telemetry this study identifies and describes local and regional scale survival and movement patterns of Central California Coast steelhead (Oncorhynchus mykiss), including their potential utilization of newly restored tidal marsh habitats in the Napa River system. Between April 8th and May 5th of 2010, 20 steelhead smolts ranging in fork length from 164 to 305 mm were collected, tagged with acoustic transmitters, and released in the upper Napa River (above tidal influence). We found no effect of release date (P?<?0.001) or size (P?<?0.005) on survival estimates based on model likelihoods. Cumulative survival from smolt release location to the Golden Gate Bridge over approximately 77 river kilometers (RKM) was 0.60 (SE?=?0.16). Reach-specific survival was lowest in the initial 30 km reach (0.70 SE?=?0.1). Survival was higher in San Pablo Bay (0.89 SE?=?0.1) and San Francisco Bay (0.96 SE?=?0.2). Sixty percent of the fish that entered the ocean were detected on a line of acoustic monitors at Point Reyes approximately 60 km north of the Golden Gate. Average movement rates of smolts were highest in San Pablo Bay (36.6 km?d^-1 SE?=?3.3) and San Francisco Bay (28.9 km?d^-1 SE?=?6.6). Smolts migrated more slowly in the river (9.0 km?d^-1 SE?=?0.9) and ocean (4.1 km?d^-1 SE?=?1.2). However, smolt movement rates in the river were dependent on location. Average movement rates of smolts were greatest shortly before their exit from the Napa River (83 km?d^-1 SE?=?13.2). Fish were not detected within the recently reconnected former salt production ponds (North, Central, and South units) adjacent to the Napa River. Based on the detection patterns of fish throughout the study area, it appears that most fish were moving at relatively high rates and were not exploring off-channel habitat.