Chaotic Behavior and Pollution Dispersion Characteristics in Engineered Tidal Embayments: A Numerical Investigation1

Abstract: This paper presents a numerical investigation of approaches to enhance the mixing and dispersion processes in tidal areas by effecting changes in the natural estuary system. It compares the impact of various estuary modifications stemming from human intervention to pollutant dispersion and chaotic flow within the estuary including the implications of alteration of the original channel shape, change of the channel bathymetry, and modification of the tidal signal. Our findings indicate that chaotic flow analysis is similar in many regards, but not all, to conventional dispersion analysis. Specifically, we conclude that (1) simplification of the flow regime reduces chaotic flow patterns and tracer particle dispersion, (2) creation of extensively protruding barriers and/or installation of barriers on opposite sides of the main stem of the estuary enhances particle dispersion and chaotic mixing, (3) installation of underwater berms has relatively minor beneficial, but highly localized, effects on chaotic regime and particle dispersion, and (4) increasing the tidal signal amplitude was shown to increase chaotic and dispersion properties of the estuarine system. A parametric study investigating the effect of several geometrical configurations and tidal signals on characteristics of chaotic flows concludes the paper.     

MODIFICATION OF NEILL'S EQUATION FOR STORM‐TIDE DESIGN FLOW ANALYSIS1

ABSTRACT: Design of bridges spanning tidal estuaries or bays requires an estimate of peak tidal flow. One common approach to estimating these flows (Neill's method) uses a first‐order approximation of uniform water surface rise in the water body. For larger water bodies, the assumptions of this method are decreasingly valid. This study develops a simple modification that accounts for the spatial variability in the response of tidal waterways to storm surge flows. The peak tidal flow predicted by Neill's equation is compared to the peak flow determined by numerical simulation of estuaries with simple geometries, ranging from 1 to 25 km in length, using the U.S. Army Corps of Engineers one‐dimensional unsteady flow model, UNET. Results indicate that, under certain conditions, it may be appropriate to apply a correction factor to the peak discharge and peak velocity predicted by Neill's method. An algorithm, developed by nonlinear regression, is presented for computing correction factors based on estuary length, shape, mean depth, and storm‐tide characteristics. The results should permit the design of more reliable, cost‐effective structures by providing more realistic estimates of the potential for bridge scour in tidal waterways, especially when a full solution of the unsteady flow equations is impractical.     

Macroalgal growth in nutrient-enriched estuaries: A biogeochemical and evolutionary perspective

Increased nutrient loading of a body of water leads to an increase in macroalgal growth. It is generally observed, however, that certain species thrive more than others, capitalising on the increased nutrient availability. These are usually small, fast-growing, ephemeral algae that often appear as nuisance blooms. This article discusses the correlation between nutrient increase and macroalgal bloom formation. From a historical perspective, the evolutionary history of nuisance macroalgae, and the habits available to them prior to anthropogenic influences on estuarine geochemistry are considered. The occurrence of macroalgal genera whose distribution is commonly related to estuaries with high nutrient loading is discussed, along with evidence suggesting that the ecophysiological traits of r-selected, ephemeral algae largely contribute to their ecological success and bloom-formation at nutrient-enriched sites.     

渤海湾两条河流及其近岸海域水体中DOM的光谱特征及影响因素

应用三维荧光光谱结合吸收光谱分析,研究了2019年夏季天津市大清河-独流减河水系和河北省黄骅市捷地减河及其河口区水体中溶解有机物（DOM）的空间分布特征、来源及其影响因素。紫外-可见光谱结果表明,研究区水体的SUVA₂₅₄与盐度有显著正相关关系;两条河流的下游水体中S_275-295均值均大于上游和中游。平行因子分析结果表明,两条河流均检测到两种类腐殖质组分C1（240,300/390 nm）和C3（260,335/477 nm）以及一种类蛋白质组分C2（225,275/339 nm）。在大清河-独流减河水系及其近岸海域水体中,这三种组分与盐度呈显著负相关关系,其中由于人为输入（TN和TP含量高,工业排污）影响导致C2与盐度的相关性弱于C1和C3。该水系水体在低盐度时C2的占比高于捷地减河,主要受到工农业废水输入与其支流子牙河汇入的共同影响,而捷地减河主要受农业废污水输入的影响。此外,自然因素（盐度、海水混合）和人为因素（人为输入、筑坝拦截）的不同导致渤海湾两条入海河流中有色溶解有机质（CDOM）的光学特性和混合行为出现显著差异。其中筑坝拦截导致独流减河坝前水体的CDOM平均分子量低于下游水体,并且增强了河口区陆源类腐殖质的去除作用。综上,三维荧光光谱结合平行因子分析能判别河流局部条件的差异对整体CDOM空间分布特征的影响,研究结果可为渤海湾地区河流及河口水体CDOM生物地球化学过程研究提供基础数据。     

高浊度河口颗粒态重金属分布特性

根据1994年6月长江口，杭州湾的水质调查资料，分析了这类高浊度河口颗粒重金属的分布规律。研究表明，在长江口和杭州湾内，悬沙中，Cu,Pb,Cd和表层沉积物中Cu,Pb,Cd分布特征相似，尤其在杭州湾中部水域，二者重金属含量呈趋同的趋势。细颗粒物质是颗粒态重 主要载体。在高浊度河口，动力沉积过程为控制颗粒态重金属分布和输移的主要因子，悬沙中重金属的分布对泥沙运动具有指示作用。     

INPUTS OF COPPER‐BASED CROP PROTECTANTS TO COASTAL CREEKS FROM PASTICULTURE RUNOFF1

ABSTRACT: Inputs of copper‐based crop protectants from tomato fields grown under plastic mulch agriculture (plasticulture) to an estuarine creek were investigated. Copper was measured in runoff from diverse land‐uses including conventional agriculture, plasticulture, residences, and natural areas. Water column and sediment copper concentrations were measured in plasticulture and control (nonagriculture) watersheds. Copper concentrations in plasticulture‐impacted creeks exceeded background levels episodically. High concentrations occurred during or immediately after runoff‐producing rains. Concentrations of 263 μg/L total copper and 126 μg/L dissolved copper were measured in a tidal creek affected by plasticulture; concentrations exceeded the shellfish LC₅₀ values and the water quality criteria of 2.9 μg/L dissolved copper. Control watersheds indicated background water column levels of ≤ 4 μg/L dissolved copper with similar copper levels during periods with and without rain. The copper concentrations in tomato plasticulture field runoff itself contained up to 238 μg/L dissolved copper. Copper concentrations in runoff from other land‐uses were less than 5 μg/L dissolved copper. Creek sediment samples adjacent to a plasticulture field contained significantly higher copper concentrations than sediments taken from nonplasticulture watersheds.     

Evaluation of a Three‐Dimensional Hydrodynamic Model Applied to Chesapeake Bay Through Long‐Term Simulation of Transport Processes

A numerical model, the Curvilinear Hydrodynamics in 3‐Dimensions, Waterway Experiment Station version (CH3D‐WES), was applied to represent transport processes of the Chesapeake Bay. Grid resolution and spatial coverage, tied with realistic bathymetry, ensured dynamic responses along the channel and near the shoreline. The model was run with the forcing ranges from high frequency astronomical tides to lower frequency meteorological forcing, given by surface wind and heat flux, as well as hydrological forcing given by fresh water inflows both from upstream and distributed sources along the shoreline. To validate the model, a long‐term simulation over seven‐year time period between 1994 and 2000 was performed. The model results were compared with existing observation data including water level time series, which spans over a wide spectrum of time scales, and long‐term variations in salinity structures over varying parts of the Bay. The validated model is set to provide an appropriate transport mechanism to the water quality model through linkage, warranting that the model takes into account the complexity in time and spatial scales associated with the dynamic processes in the Chesapeake.     

Sources of Suspended-Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model1

Brakebill, John W., Scott W. Ator, and Gregory E. Schwarz, 2010. Sources of Suspended-Sediment Flux in Streams of the Chesapeake Bay Watershed: A Regional Application of the SPARROW Model. Journal of the American Water Resources Association (JAWRA) 46(4): 757-776. DOI: 10.1111/j.1752-1688.2010.00450.x Abstract: We describe the sources and transport of fluvial suspended sediment in nontidal streams of the Chesapeake Bay watershed and vicinity. We applied SPAtially Referenced Regressions on Watershed attributes, which spatially correlates estimated mean annual flux of suspended sediment in nontidal streams with sources of suspended sediment and transport factors. According to our model, urban development generates on average the greatest amount of suspended sediment per unit area (3,928 Mg/km²/year), although agriculture is much more widespread and is the greatest overall source of suspended sediment (57 Mg/km²/year). Factors affecting sediment transport from uplands to streams include mean basin slope, reservoirs, physiography, and soil permeability. On average, 59% of upland suspended sediment generated is temporarily stored along large rivers draining the Coastal Plain or in reservoirs throughout the watershed. Applying erosion and sediment controls from agriculture and urban development in areas of the northern Piedmont close to the upper Bay, where the combined effects of watershed characteristics on sediment transport have the greatest influence may be most helpful in mitigating sedimentation in the bay and its tributaries. Stream restoration efforts addressing floodplain and bank stabilization and incision may be more effective in smaller, headwater streams outside of the Coastal Plain.     

URBAN WATER MANAGEMENT AND COASTAL WETLAND PROTECTION IN COLLIER COUNTY,FLORIDA1

ABSTRACT: Traditional development in South Florida has in many cases resulted in undesirable degradation of terrestrial and aquatic ecosystems, due to overdrainage and overenrichment of surface waters. The study described in this paper was undertaken in order to establish guidelines under which urban development may take place in coastal areas, while minimizing unwanted environmental changes. The study area consists of approximately 70 square miles of relatively flat land in Collier County, Florida. The coastal wetlands of the region are a highly valued natural resource containing the Rookery Bay Wildlife Sanctuary. The upland properties are mainly pine woodlands and have great potential for development. A master plan was developed which will (1) provide adequate drainage for existing and projected development within the study area and (2) maintain the integrity of the estuarine zone. The major recommendations of the plan relate to land use, physical control of surface waters, including construction and maintenance of the water management system, and implementation of the plan.     

Interactions of warming and altered nutrient load timing on the phenology of oxygen dynamics in Chesapeake Bay

The effects of nutrient loading on estuaries are well studied, given the multitude of negative water quality and ecosystem effects that have been attributed to excess nitrogen and phosphorus. A current gap in this knowledge involves the sensitivity of seasonal cycles of estuarine biogeochemical processes to direct (warming) and indirect influences (nutrient load timing) of climate change. We used a coupled hydrologic–biogeochemical model to investigate changes in the phenology of hypoxia and related biogeochemical processes in Chesapeake Bay under three different hydrologic regimes. Shifts to earlier nutrient load timing during idealized simulations reduced the overall annual hypoxic volume, resulting from discernable, but relatively small reductions in phytoplankton biomass and both sediment and water-column respiration. Simulated increases in water temperature caused an increase in spring/early summer hypoxic volume associated with elevated respiration rates, but an associated exhaustion of organic matter in the early summer caused a decrease in late summer/fall hypoxic volume due to lowered respiration. Warming effects on hypoxia were larger than nutrient timing effects in scenarios where warming was restricted to spring and when it was applied to all months of the year. These idealized simulations begin the process of understanding the potential impacts of future climatic changes in the seasonal timing of key biogeochemical processes associated with eutrophication.