Wind-driven Sediment Resuspension Research Articles

Coral geochemical response to uplift in the aftermath of the 2005 Nias–Simeulue earthquake

On 28 March 2005, the Indonesian islands of Nias and Simeulue experienced a powerful Mw 8.6 earthquake and coseismic uplift and subsidence. In areas of coastal uplift (up to ~ 2.8 m), fringing reef coral communities were killed by exposure, while deeper corals that survived were subjected to habitats with altered runoff, sediment and nutrient regimes. Here we present time-series (2000–2009) of Mn/Ca, Y/Ca and Ba/Ca variability in massive Porites corals from Nias to assess the environmental impact of a wide range of vertical displacement (+ 2.5 m to − 0.4 m). High-resolution LA-ICP-MS measurements show that skeletal Mn/Ca increased at uplifted sites, regardless of reef type, indicating a post-earthquake increase in suspended sediment delivery. Transient and/or long-term increases in skeletal Y/Ca at all uplift sites support the idea of increased sediment delivery. Coral Mn/Ca and Ba/Ca in lagoonal environments highlight the additional influences of reef bathymetry, wind-driven sediment resuspension, and phytoplankton blooms on coral geochemistry. Together, the results show that the Nias reefs adapted to fundamentally altered hydrographic conditions. We show how centuries of repeated subsidence and uplift during great-earthquake cycles along the Sunda megathrust may have shaped the modern-day predominance of massive scleractinian corals on the West Sumatran reefs.

Water surface albedo and its driving factors on the turbid lakes of Northeast China

Lake water surface albedo (LWSA) is a critical parameter for describing energy flux balance at the air–water interface. It is used to measure the capacity of lake water surface reflectance in the shortwave radiation band, which controls the energy partitioning between atmosphere and lake. LWSA and its driving factors, including solar radiation angle, water quality and meteorology, in lakes of Northeast China was analyzed in this research. Solar altitude angle emerged as the most important controlling factor of LWSA. The results showed a strong reduction in LWSA values with increase in solar altitude angle. The study also documented a strong effect of suspended matter on the radiative properties of lakes surface, leading to increased LWSA with increased in suspended matter concentration, especially at high solar altitude angles (R2: 0.76). While no significant association (R2: 0.11) was found between LWSA and chlorophyll-a concentration, LWSA was positively correlated with wind speed (R2 of 0.62 and 0.50 at high and low solar altitude angles, respectively), likely a consequence of wind-driven sediment resuspension in lake waters. Although chromophoric dissolved organic matter (CDOM) and organic particulate matter can affect energy partitioning and spectral distribution of incident solar radiation in lake waters, there was insufficient evidence of measurable effects on LWSA. Variations in LWSA recorded in this study were primarily dependent on similar solar altitude angles and backscattering properties of inorganic particulate matter suspended in the water column. Higher surface albedo was found in the turbid lakes.

Wind-Driven Sediment Resuspension in the World's Fourth Largest Lake Contributes Substantial Phosphorus Load to the 11th Largest Lake.

Capturing precipitation-based episodes is a longstanding issue for estimating tributary loads; however, wind-driven resuspension in Lake Huron creates similar uncertainties in its estimated load to Lake Erie. Recent suggestions that the phosphorus load from Lake Huron is underestimated because sampling frequencies miss contributions from resuspension events are speculative because they did not include direct load measurements, address all resuspension regions, or assess the potential bioavailability of the load. We address these shortcomings by evaluating Lake Huron's nearshore regions, characterizing the biological availability of the load, and providing direct comparisons of load estimates with and without the resuspended load. We show that total phosphorus concentrations in Lake Huron and the St. Clair River are higher during resuspension events and that bioavailability of that material is comparable to that reported elsewhere. New load estimates, based on continuous turbidity measurements converted to phosphorus through P-turbidity relationships, were almost 90% higher than traditional load estimates, providing empirical evidence for the significantly underestimated previous load. This confirmation is important because if the Lake Huron load is not decreased, reductions from other sources would be needed to meet the overall reduction targets set by the binational Great Lakes Water Quality Agreement.

Multi-decadal changes in phytoplankton biomass in northern temperate lakes as seen through the prism of landscape properties.

Ecologists collectively predict that climate change will enhance phytoplankton biomass in northern lakes. Yet there are unique variations in the structures and regulating functions of lakes to make this prediction challengeable and, perhaps, inaccurate. We used archived Landsat TM/ETM+satellite products to estimate epilimnetic chlorophyll-a (Chl-a) concentration as a proxy for phytoplankton biomass in 281 northern temperate lakes over 28years. We explored the influence of climate (air temperature, precipitation) and landscape proxies for nutrient sources (proportion of wetlands in a contributing catchment, size of the littoral zone, potential for wind-driven sediment resuspension as estimated by the dynamic ratio) or nutrient sinks (lake volume) in a random forest model to explain heterogeneity in peak Chl-a. Lakes with higher Chl-a (median Chl-a=2.4μgL-1 , n=40) had smaller volumes (<44×104 m3 ) and were more sensitive to increases in temperature. In contrast, lakes with lower Chl-a (median Chl-a=0.6μgL-1 , n=241) had larger volumes (≥44×104 m3 ), contributing catchments with smaller proportions of wetlands (<4.5% of catchment area, n=70), smaller littoral zones (<16.4ha, n=137), minimal wind-driven sediment resuspension (as defined by the dynamic ratio; <0.45, n=232), and were more sensitive to increases in precipitation. Lakes with larger volumes were generally less responsive to climate factors; however, larger volume lakes with a significant proportion of wetlands and larger littoral zones behaved similarly to lakes with smaller volumes. Our finding that lakes with different landscape properties respond differently to climate factors may help predict the susceptibility of lakes to eutrophication under changing climatic conditions.

Water quality dynamics of floodplain lakes in relation to river flooding and cattle grazing

Floodplain water quality is naturally regulated by river floods, but is increasingly affected by anthropogenic activities. Accordingly, we evaluated the combined influence of river flooding (pre- and post-flood periods) and rotational grazing (cattle presence or absence) on water quality of floodplain lakes. We hypothesised that river floods decrease the concentrations of most water constituents and dilute grazing effects on water quality, and that differences in cattle pressure (i.e. grazing duration) promote differences in water quality among lakes. Nutrient concentration decreased after the flood through washing-out and dilution, but other water constituents showed different responses. Contrary to expectations, water-quality changes in relation to cattle presence or absence occurred only after the flood, with higher turbidity and phosphorus during periods with than without cattle. Finally, water-quality variability among lakes was attributed to their different sizes (and therefore dilution capacities), but not to differences in cattle pressure. Our results suggest that river–floodplain connectivity and grazing location in areas with large lakes are important for preserving water quality. Pre-flood changes in water quality in relation to cattle presence or absence could have been obscured by wind-driven sediment resuspension, which has important effects during shallow-water stages, and by high phosphorus concentration, which can prevent removal during periods without cattle.

Spatial differences in wind-driven sediment resuspension in a shallow, coastal estuary

Two locations approximately 11 km apart along the axis of the New River Estuary near Jacksonville, NC USA were continuously monitored for eight years. Included in the observations are vertical profiles of turbidity, temperature, salinity, chl-a, dissolved oxygen, pH and water velocity as well as local wind velocity. Differences between the two sites result from a number of factors, including bathymetry, wind strength, direction and fetch, estuarine morphology, tidal currents and sediment properties. The site near the head of the estuary, Morgan Bay, is deeper, experiences generally weaker winds and has less fetch in most directions. Stones Bay, the down-estuary site, is shallower, experiences stronger winds and has longer fetch, particularly in the prevailing wind directions. Current speeds also differ along the estuary with the down-estuary Stones Bay site being more tidal.The observations were used together with a simple wave model to analyze the estuarine turbidity response to different forcing mechanisms. Results suggest that sediments are resuspended primarily by wind-wave generated bottom stress at both locations. While turbidity is generally higher in Stones Bay than in Morgan Bay, turbidity as a function of the local wave-induced bottom stress (including forcing from all directions) is similar at both locations at low stress but diverges at higher stresses. At higher bottom stresses, turbidity in Stones Bay responds primarily to winds from the NE, S and NW while turbidity in Morgan Bay responds primarily to winds from the NW and S. Accounting for sediment resuspension within an approximate spatial advection scale around each of the observation sites, yields a similar turbidity vs bottom stress response curve for the three primary directions in Stones Bay and the S direction in Morgan Bay but a greater turbidity response for winds from the NW in Morgan Bay. In the latter case, waves are crossing the section of the New River Estuary just downstream of the confluence with the New River and are presumably encountering sediments that are more easily resuspended.Average sediment export is down-river with more sediment leaving Stones Bay than Morgan Bay.

Long-term patterns of benthic irradiance and kelp production in the central Beaufort sea reveal implications of warming for Arctic inner shelves

This study synthesizes a multidecadal dataset of annual growth of the Arctic endemic kelp Laminaria solidungula and corresponding measurements of in situ benthic irradiance from Stefansson Sound in the central Beaufort Sea. We incorporate long-term data on sea ice concentration (National Sea Ice Data Center) and wind (National Weather Service) to assess how ice extent and summer wind dynamics affect the benthic light environment and annual kelp production. We find evidence of significant changes in sea ice extent in Stefansson Sound, with an extension of the ice-free season by approximately 17 days since 1979. Although kelp elongation at 5–7 m depths varies significantly among sites and years (3.8–49.8 cm yr−1), there is no evidence for increased production with either earlier ice break-up or a longer summer ice-free period. This is explained by very low light transmittance to the benthos during the summer season (mean daily percent surface irradiance ± SD: 1.7 ± 3.6 to 4.5 ± 6.6, depending on depth, with light attenuation values ranging from 0.5 to 0.8 m−1), resulting in minimal potential for kelp production on most days. Additionally, on month-long timescales (35 days) in the ice-free summer, benthic light levels are negatively related to wind speed. The frequent, wind-driven resuspension of sediments following ice break-up significantly reduce light to the seabed, effectively nullifying the benefits of an increased ice-free season on annual kelp growth. Instead, benthic light and primary production may depend substantially on the 1–3 week period surrounding ice break-up when intermediate sea ice concentrations reduce wind-driven sediment resuspension. These results suggest that both benthic and water column primary production along the inner shelf of Arctic marginal seas may decrease, not increase, with reductions in sea ice extent.

Spatial differences in wind-driven sediment resuspension in a shallow, coastal estuary

Spatial differences in wind-driven sediment resuspension in a shallow, coastal estuary

Effects of internal loading on phosphorus distribution in the Taihu Lake driven by wind waves and lake currents

Wind-driven sediment resuspension exerts significant effects on the P behavior in shallow lake ecosystems. In this study, a comprehensive dynamic phosphorus (P) model that integrates hydrodynamic, wind wave and sediment transport is proposed to assess the importance of internal P cycling due to sediment resuspension on water column P levels. The primary contribution of the model is detailed modeling and rigorous coupling of sediment and P dynamics. The proposed model is applied to predict the P behavior in the shallow Taihu Lake, which is the third largest lake in China, and quantitatively estimate the effects of wind waves and lake currents on P release and distribution. Both the prevailing southeast winds in summer and northwest winds in winter are applied for the simulation, and different wind speeds of 5 m/s and 10 m/s are also considered. Results show that sediment resuspension and the resulting P release have a dominant effect on P levels in Taihu Lake, and likely similar shallow lakes. Wind-driven waves at higher wind speeds significantly enhance sediment resuspension and suspended sediment concentration (SSC). Total P concentration in the water column is also increased but not in proportion to the SSC. The different lake circulations resulting from the different prevailing wind directions also affect the distribution of suspended sediment and P around the lake ultimately influencing where eutrophication is likely to occur. The proposed model demonstrates that internal cycling in the lake is a dominant factor in the lake P and must be considered when trying to manage water quality in this and similar lakes. The model is used to demonstrate the potential effectiveness of remediation of an area where historical releases have led to P accumulation on overall lake quality.

Seasonal nearshore sediment resuspension and water clarity at Lake Tahoe

Reardon KE, Moreno-Casas PA, Bombardelli FA, Schladow SG. 2016 Seasonal nearshore sediment resuspension and water clarity at Lake Tahoe. Lake Reserv Manage. 32:132--145.Motivated by management challenges due to declining water clarity at Lake Tahoe, California–Nevada, we synthesized field observations and modeling of wind-driven nearshore sediment resuspension to inform decision-makers. We present the first field observations of nearshore sediment resuspension in both summer and winter and investigate seasonal differences in lake behavior. In addition, using a previously modified and validated wind-wave model, STWAVE, we developed management charts that illustrate relationships between fetch, wind intensity, and wave height and between water depth, wave height, and the potential for mobilization of different-sized particles. For a representative grain size of 150 μm, the wind-driven surface waves were found to influence the sediments to a maximum water depth of 9 m. Additionally, we evaluated the potential for wind-driven nearshore sediment resuspension with changing lake levels, considering a range of possible future scenarios. The areal extent of potential wind-driven sediment resuspension in Lake Tahoe's southern nearshore zone is maximum (8.3 km2) at a lake water level equal to the natural rim (1897 m). The potential for resuspension notwithstanding, the results demonstrated no increase in particle loading of the size class identified to most negatively impact water clarity (<16 μm). Therefore, we corroborate previous findings and conclude that wind-driven nearshore sediment resuspension does not contribute to the declining water clarity of Lake Tahoe and attribute this to a lack of available fine material within the lake sediments.

Sediment resuspension in a shallow lake with muddy substrates: St Lucia, South Africa

Wind-driven sediment resuspension affects the physical and biological environment of the water column in shallow estuarine lakes. This study investigated the relationship between wind-driven waves and suspended sediment concentration (SSC) using the 33km2 South Lake basin of Lake St Lucia, South Africa as a case study. Five wave poles measuring significant wave height and turbidity were deployed over an aggregate period of twenty days at distributed locations where sediment substrate compositions varied from muddy to sandy and depths ranged from 0.7m to 2.1m. The resulting turbidity dynamics were used to test a simple depth-averaged model of suspended sediment concentrations. The model performed best in the muddy regions of the lake and was able to simulate the resuspension dynamics more accurately than the settling dynamics. Peak suspended sediment concentration levels were best captured for the deeper muddy locations. The model provides a means to make spatially explicit predictions of suspended sediment concentrations that can be used to understand the forcing mechanisms for primary producer growth and distribution or to improve sediment budget calculations.

Water quality changes following nutrient loading reduction and biomanipulation in a large shallow subtropical lake, Lake Griffin, Florida, USA

Lake Griffin received discharges for decades from muck farms developed on former floodplain wetlands, leading to hypereutrophic conditions. Management actions included wetland restoration of farmland to reduce nutrient discharges, and harvesting of gizzard shad to remove nutrients in fish biomass and reduce nutrient recycling from sediments. Despite a reported susceptibility to wind-driven sediment resuspension, there have been substantial improvements in water quality in Lake Griffin, including decreases in nutrient concentrations, chlorophyll-a, and cyanobacterial biovolume, and increases in water transparency. Water quality improvements in Lake Griffin were substantially greater than occurred in ten comparison lakes. External nutrient load reduction was the primary factor contributing to water quality improvement, although there was evidence of an effect of shad harvesting, including correlations between shad catch per unit effort and nutrient concentrations, and an estimated effect of biomass removal and recycling reduction accounting for about 40% of the external load during the harvest period. Net production of total nitrogen in the lake was strongly related to external total phosphorus loading, indicating phosphorus limitation of nitrogen fixation. The response of Lake Griffin indicates that the combination of external nutrient load reduction and biomanipulation can result in sustained improvements in water quality in shallow subtropical lakes.

Lake topography and wind waves determining seasonal-spatial dynamics of total suspended matter in turbid Lake Taihu, China: assessment using long-term high-resolution MERIS data.

Multiple comprehensive in situ bio-optical investigations were conducted from 2005 to 2010 and covered a large variability of total suspended matter (TSM) in Lake Taihu to calibrate and validate a TSM concentration estimation model based on Medium Resolution Imaging Spectrometer (MERIS) data. The estimation model of the TSM concentration in Lake Taihu was developed using top-of-atmosphere (TOA) radiance of MERIS image data at band 9 in combination with a regional empirical atmospheric correction model, which was strongly correlated with the in situ TSM concentration (r 2 = 0.720, p<0.001, and n = 73). The relative root mean square error (RRMSE) and mean relative error (MRE) were 36.9% and 31.6%, respectively, based on an independent validation dataset that produced reliable estimations of the TSM concentration. The developed algorithm was applied to 50 MERIS images from 2003 to 2011 to obtain a high spatial and temporal heterogeneity of TSM concentrations in Lake Taihu. Seasonally, the highest and lowest TSM concentrations were found in spring and autumn, respectively. Spatially, TSM concentrations were high in the southern part and center of the lake and low in Xukou Bay, East Lake Taihu. The lake topography, including the water depth and distance from the shore, had a significant effect on the TSM spatial distribution. A significant correlation was found between the daily average wind speed and TSM concentration (r 2 = 0.685, p<0.001, and n = 50), suggesting a critical role of wind speed in the TSM variations in Lake Taihu. In addition, a low TSM concentration was linked to the appearance of submerged aquatic vegetation (SAV). Therefore, TSM dynamics were controlled by the lake topography, wind-driven sediment resuspension and SAV distribution.

Remote sensing of diffuse attenuation coefficient of photosynthetically active radiation in Lake Taihu using MERIS data

Especially for a shallow and extremely turbid lake, light availability in the water column can determine the euphotic zone, and the horizontal and vertical distribution of algae species. Light attenuation is traditionally quantified as the diffuse attenuation coefficient of the photosynthetically available radiation (Kd(PAR)). Global coverage of Kd(PAR) at high spatial and temporal resolution can be provided by satellite measurements, and these data can be used to improve our understanding of the physical, chemical and biological processes in Lake Taihu, a large shallow lake in China, of considerable importance as a source of drinking water for several large cities.The primary dominated contributor to Kd(PAR) was determined firstly using linear regression. There was a significant positive correlation between Kd(PAR) and concentrations of total suspended matter (TSM). The determination coefficient between Kd(PAR) and TSM (R2=0.91) was significantly higher than that between Kd(PAR) and chlorophyll-a concentrations (Chl-a) (R2=0.11), and between Kd(PAR) and absorption of chromophoric dissolved organic matter (CDOM) (R2=0.01). Our results therefore could demonstrate that TSM usually plays a dominant role in the attenuation of light in Lake Taihu.A retrieval model of Kd(PAR) values for Lake Taihu was subsequently developed using top-of-atmosphere (TOA) radiance of Medium Resolution Imaging Spectrometer (MERIS) image data at band 10, which was strongly correlated with in situ Kd(PAR) (R2=0.74, p<0.005, N=48). In contrast, the atmospheric corrected reflectance of MERIS image data was not strongly correlated with in situ Kd(PAR). Thus, atmospheric correction was not a prerequisite for estimations of Kd(PAR) in this highly turbid and hyper-eutrophic lake, and a simple empirical model of the Kd(PAR) estimation for Lake Taihu was effective.With the simple model, the seasonal and spatial distributions of Kd(PAR) in Lake Taihu were studied using the MERIS measurements from 2003 to 2010. Our results show distinct seasonal, spatial, and wind driven, Kd(PAR) values in Lake Taihu. The highest and the lowest Kd(PAR) values were found in summer and in winter, respectively. The increase of Kd(PAR) in summer can be attributed to the phytoplankton blooms, and wind-driven sediment resuspension. Spatially, the Kd(PAR) values were high in the southern part and the lake center, and low Kd(PAR) in East Lake Taihu. Based on the MERIS derived Kd(PAR) values, a significant correlation was found between Kd(PAR) and wind speeds, suggesting a critical role of wind speeds in the Kd(PAR) variations in Lake Taihu.

Chloride and total phosphorus budgets for Green Bay, Lake Michigan

Green Bay is an elongated freshwater embayment located in northwestern Lake Michigan. Due to its short residence time, the lower bay is heavily influenced by the Fox River's large nutrient load. The inner bay is classified as hypereutrophic and a well-defined trophic gradient is observed moving away from the Fox River towards Lake Michigan, where the bay is nearly oligotrophic. Recent chloride and total phosphorus loading estimates were used to update a chloride and total phosphorus mass-balance model for the bay for 1994–2008. The chloride model provided a means to estimate turbulent eddy diffusion within the bay and exhibited excellent agreement with observed data. The total phosphorus model agreement with observed data was generally good, with the exception of a large deviation in lower Green Bay during 1999–2004. The model was used to estimate the internal loadings necessary to account for the deviation in phosphorus concentrations. The source of the unexpected increase remains unclear, but we speculate significant internal loading due to wind-driven sediment resuspension and hypoxia-induced phosphorus diffusion was significant. These models allow needed reductions to be identified and sourced and also indicate the role internal loading may play in the Green Bay phosphorus budget.

A one‐dimensional eco‐geomorphic model of marsh response to sea level rise: Wind effects, dynamics of the marsh border and equilibrium

In this study we investigate the long term evolutionary trend of tidal marshes and their possible tendency to approach equilibrium. We account of the dynamic interaction between the marsh and its adjacent environment, allowing for both variations of marsh elevation and displacement of the marsh boundary. We thus consider a 1‐D configuration consisting of a tidal channel merging into a 1‐D marsh. Starting from some initial configuration of the channel we model how a salt marsh forms at the landward end of the channel and determine the long term evolution of the channel ‐ marsh configuration under different scenarios of relative sea level rise. Previously established results on the morphodynamic evolution of a tidal channel are extended accounting for the effects of vegetation and wind driven sediment resuspension in regions where tidal stresses are too weak to mobilize sediments. Results suggest that, for sufficiently low rates of relative sea level rise the marsh platform may be able to reach an equilibrium elevation, provided wind resuspension is able to maintain a sufficiently large sediment concentration close to the marsh boundary. This is in general agreement with recent results based on zero dimensional modeling. However, we find that the marsh boundary is unstable, as progradation or retreat is generally experienced depending on a delicate balance between tidal transport and transport driven by wind setup. In this sense, actual morphodynamic equilibrium is a rather exceptional and unstable state.

Random forest algorithm yields accurate quantitative prediction models of benthic light at intertidal sites affected by toxic Lyngbya majuscula blooms

It is shown that targeted high frequency monitoring and modern machine learning methods lead to highly predictive models of benthic light flux. A state-of-the-art machine learning technique was used in conjunction with a high frequency data set to calibrate and test predictive benthic lights models for sites dominated by the toxic cyanobacterium Lyngbya majuscula. Datasets of incident light flux, waters depth, wind speed, wind direction and benthic light flux were collected at two sites, Deception Bay and Eastern Banks, in Moreton Bay, Queensland, that are affected by the toxic marine cyanobacteria L. majuscula. Random forest models were calibrated and validated using the dataset. The models predict benthic photosynthetically active radiation (PAR) based on wind speed, wind direction, water depth and incident light. The two benthic light models produced have high predictive capacity with R2 values of the order 0.8 for both calibration and validation. Wind speed and/or direction influenced the prediction of benthic PAR in the model at each site, suggesting that wind-driven sediment resuspension is an important process in controlling water clarity and hence benthic PAR at both sites; a result consistent with many previous examples from coastal regions. In particular, wind direction had a marked affect on benthic PAR at the partially sheltered Deception Bay site compared to the fully exposed Eastern Banks site. Consistent with other Harmful Algae Bloom (HAB) species, eutrophication has been identified as a common link between sites affected by L. majuscula blooms. However, we show here that at least one major bloom of L. majuscula in Deception Bay coincided with light conditions for optimal L. majuscula photosynthesis, supporting the hypothesis that toxic blooms are a result of a confluence of causes rather than just one. We argue that at eutrophied sites, variation in parameters such as temperature and light rather than nutrients are more likely to cause blooms. This study demonstrates that collection of high frequency variables related to aquatic light flux combined with state of the art machine learning techniques, such as the random forest algorithm, can produce highly accurate models of light flux at shallow coastal sites. These models provide management with the beginnings of an early warning system and scientists with a practical tool for catching the bloom at the incipient stage rather than after the bloom has already developed.

基于VGPM模型和MODIS数据估算梅梁湾浮游植物初级生产力

Phytoplankton is typically the most important primary producer in lake ecosystems,strongly influences nutrient concentrations,and supports higher trophic levels such as zooplankton and filter-feeders.Knowledge of primary production,and its spatial and temporal variations,is of special relevance for Meiliang Bay in the northern part of the Lake Taihu,China,which has three important inflowing rivers which carry domestic sewage and industrial waste water from the adjacent cities of Changzhou and Wuxi.Although primary production in oceans had frequently been estimated using the Vertically Generalized Production Model(VGPM),this approach has rarely been used in inland lakes.In our present study,phytoplankton primary production in Meiliang Bay,Lake Taihu,was estimated from February to December in 2009 based on VGPM using the MODIS-derived data for chlorophyll a,total suspended solid concentrations,and water surface temperature. There were significant spatial variations in the monthly mean daily primary production in 3 of the 4 seasons: spring(March,April,May),summer(June,July,August),and autumn(September,October,November),and primary production gradually decreased from inner Meiliang Bay to outer Meiliang Bay.In inner Meiliang Bay,suitable qualities and quantities of nutrients,photosynthetically available radiation,and water temperature,provided good conditions for algal growth in these three seasons.However,there was no significant spatial variation in the monthly mean daily primary production in winter(February,December) due to the death and degradation of algae in the whole of Meiliang Bay.There was however,significant spatial variation in the annual mean daily primary production in Meiliang Bay,Lake Taihu in 2009. Time series analysis showed that the seasonal variation of primary production was: summer autumn spring winter.The annual mean daily primary production was 1,291.61 mgC · m-2 · d-1,with the highest primary production in August.The trend in temporal variations of the primary production in Meiliang Bay was consistent with that of the chlorophyll a concentration.Temproal variations in primary production were less closely linked to water temperatures which peaked in June and August,and to photosynthetic available radiation intensity which peaked in July. To explore the effect caused by the sediment resuspension,the phytoplankton primary production estimated by the VGPM model in Meiliang Bay was normalized to per chlorophyll a concentration,water temperature,and photosynthetically available radiation intensity.A significant negative relationship was found between the total suspended solid concentration and the normalized primary production,and a power function relationship was also found between them with a determination coefficient value of 0.487 by non-linear curve fitting.Thus,it could be demonstrated that the increase of total suspended solid concentration from wind-driven sediment resuspension could cause primary production to decrease markedly.The mean maximum carbon fixation rate was(6.48±0.17) mgC · mgChla-2 · h-1 when the water temperature ranged from 19℃ to 21℃.Furthermore,water temperature was significantly and positively correlated to primary production in Meiliang Bay.A positive correlation was found between water temperature and the maximum carbon fixation rate when water temperature was less than 21℃.

Characterizations of individual suspended mineral particles in western Lake Erie: Implications for light scattering and water clarity

Light-scattering attributes of minerogenic particles from the water column of the western basin of Lake Erie (13 sites, plus one from the central basin and one from Sandusky Bay), collected after a wind event, were characterized by scanning electron microscopy interfaced with automated image and X-ray analyses (SAX). SAX results specified scattering attributes for individual particles, including size and chemical composition, and were used in forward Mie theory calculations of minerogenic scattering and backscattering coefficients (bm and bb,m). Clay mineral particles, in the size range of 1–20μm, were the dominant form of minerogenic scattering, representing >75% of bm and bb,m. Levels of bm and bb,m were high in the western basin, apparently in part due to wind-driven sediment resuspension, and wide spatial variability was observed. The credibility of the SAX-Mie estimates of bm and bb,m was supported by the extent of optical closure obtained with paired bulk measurements of particulate scattering and backscattering coefficients (bp and bbp), and independent estimates of organic particle contributions based on empirical bio-optical models. Minerogenic particles dominated bp and particularly bbp, and regulated spatial differences in the related common metrics of optical water quality, including turbidity and clarity. The bbp:bp ratio was found to be a good predictor of the spatial differences in the relative contributions of minerogenic particles versus phytoplankton to scattering.

Effects of resuspension and eutrophication level on summer phytoplankton dynamics in two hypertrophic areas of Lake Taihu, China

The composition of summer phytoplankton communities in two highly eutrophic areas of Lake Taihu, a large, shallow water body in China (area 2,338 km2; mean depth 2.0 m), was studied in relation to selected environmental variables. Both areas have multiple uses, including drinking water supply, fisheries, and recreation. The first area, Meiliang Bay, is much closer to central lake and subjected to wind-driven sediment resuspension, while the second, at Wuli Lake, is less affected by wave action but is considered more nutrient-rich due to its proximity to human inhabitation. By comparing two lake areas, we attempt to advance the understanding and management of different regions of shallow lakes, mainly differing in resuspension levels and eutrophication levels. A comparison of these two lake areas indicated a higher standing crop of phytoplankton in Wuli Lake than in Meiliang Bay. Canonic Correspondence Analysis indicated that nutrient status and sediment resuspension were the principal factors influencing phytoplankton composition in both areas. The dominant algal group in Meiliang Bay comprised immobile R-type strategists (Reynolds in Growth and reproductive strategies of freshwater phytoplankton, 1988), including filamentous diatoms and green algae (Aulacoseira granulate and Planctonema lauterbornii), and recruitment-beneficial RS-type strategists, mainly the colonial cyanobacteria (Microcystis spp.). The community of Wuli Lake was dominated by S-strategists, principally motile flagellates (Cryptomonas spp.) and C-strategists including small nonmotile centric diatoms and chlorococcal green algae.