Simulating vegetation effects on flows in 3D using an unstructured grid model: model development and validation

Ocean Dynamics - Prevalence of vegetation (either submerged or emergent) in shallow water significantly affects the flow and turbulence structure in this environment. In this paper, we develop a...     

基于微增模型的海洋可控源电磁法三维非结构化矢量有限元数值模拟

为了分析海洋中含金属矿的储油气砂层的成分、结构对于海洋可控源电磁场的影响特征,引入多相微增等效介质模型,结合非结构化网格实现了海洋可控源电磁三维矢量有限元正演.首先对多相微增模型进行了介绍,并分析不同参数影响下的等效电导率变化特征.而后,详细推导了频率域可控源电磁法非结构化矢量有限元方程.接着,利用预处理的IDR（s）迭代算法求解线性方程组.最后设计典型的海洋地电模型,通过正演计算,验证了本文算法的正确性和有效性,同时研究了海洋储油砂层中的金属矿的含量、孔隙度、含水饱和度等参数对于可控源电磁场响应特征的影响.

     

Multi-scale modeling of Puget Sound using an unstructured-grid coastal ocean model: from tide flats to estuaries and coastal waters

Water circulation in Puget Sound, a large complex estuary system in the Pacific Northwest coastal ocean of the United States, is governed by multiple spatially and temporally varying forcings from tides, atmosphere (wind, heating/cooling, precipitation/evaporation, pressure), and river inflows. In addition, the hydrodynamic response is affected strongly by geomorphic features, such as fjord-like bathymetry and complex shoreline features, resulting in many distinguishing characteristics in its main and sub-basins. To better understand the details of circulation features in Puget Sound and to assist with proposed nearshore restoration actions for improving water quality and the ecological health of Puget Sound, a high-resolution (around 50 m in estuaries and tide flats) hydrodynamic model for the entire Puget Sound was needed. Here, a three-dimensional circulation model of Puget Sound using an unstructured-grid finite volume coastal ocean model is presented. The model was constructed with sufficient resolution in the nearshore region to address the complex coastline, multi-tidal channels, and tide flats. Model open boundaries were extended to the entrance of the Strait of Juan de Fuca and the northern end of the Strait of Georgia to account for the influences of ocean water intrusion from the Strait of Juan de Fuca and the Fraser River plume from the Strait of Georgia, respectively. Comparisons of model results, observed data, and associated error statistics for tidal elevation, velocity, temperature, and salinity indicate that the model is capable of simulating the general circulation patterns on the scale of a large estuarine system as well as detailed hydrodynamics in the nearshore tide flats. Tidal characteristics, temperature/salinity stratification, mean circulation, and river plumes in estuaries with tide flats are discussed.     

Differential presence of anthropogenic compounds dissolved in the marine waters of Puget Sound, WA and Barkley Sound, BC

Organic compounds were evaluated in March 2010 at 22 stations in Barkley Sound, Vancouver Island Canada and at 66 locations in Puget Sound. Of 37 compounds, 15 were xenobiotics, 8 were determined to have an anthropogenic imprint over natural sources, and 13 were presumed to be of natural or mixed origin. The three most frequently detected compounds were salicyclic acid, vanillin and thymol. The three most abundant compounds were diethylhexyl phthalate (DEHP), ethyl vanillin and benzaldehyde (∼600 ng L⁻¹ on average). Concentrations of xenobiotics were 10-100 times higher in Puget Sound relative to Barkley Sound. Three compound couplets are used to illustrate the influence of human activity on marine waters; vanillin and ethyl vanillin, salicylic acid and acetylsalicylic acid, and cinnamaldehyde and cinnamic acid. Ratios indicate that anthropogenic activities are the predominant source of these chemicals in Puget Sound.     

Perfluorinated compounds in the surface waters of Puget Sound,Washington and Clayoquot and Barkley Sounds,British Columbia

Perfluorinated compounds (PFCs) are persistent organic contaminants detected in various environmental matrices including sediment, air, biota, and water. The objectives of this study was to evaluate the occurrence of these contaminants within the surface waters of the Pacific Northwest region and through relative concentrations and ratios, to assess their possible sources. Surface waters were extracted and analyzed by liquid chromatography tandem mass spectrometry (LCMSMS). Perfluoroheptanoic acid (PFHpA), perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS) were the most commonly detected PFCs. Total PFC concentrations detected ranged from 1.5 to 41 ng L-1. Surprisingly, levels of PFCs in the more urbanized Puget Sound waters were comparable to those measured from the more rural region of Clayoquot and Barkley Sounds in British Columbia. The ratio of PFHpA/PFOA were also similar between the two regions, suggesting that the burden of PFCs throughout the region results from direct input from regional sources.     

Variations of phytoplankton productivity and biomass over an annual cycle in Saanich Inlet,a British Columbia fjord

Saanich Inlet is a highly productive temperate fjord with the capability to record inter-annual patterns of water-column primary production in undisturbed laminated sediments. We investigated spatial and temporal variations in primary productivity, total and size-fractionated phytoplankton chl a, dissolved nutrients, temperature and salinity at the head and mouth of Saanich Inlet from May 2005 to November 2006. New primary productivity was also measured from May to October 2006. During the growing season (spring, summer and fall), primary productivity was 1.5 times higher at the mouth than at the head of Saanich Inlet and, averaged across stations, total productivity was 460 g C m⁻² y⁻¹. Average new productivity was 53% and 58% of total primary productivity at the head and mouth of the inlet, respectively, and during the growing season micro-phytoplankton (>20 μm; mainly diatoms) was the most abundant size-class of phytoplankton. These rates of primary production are as high as or higher than those measured in other fjords, possibly because of a tidally-driven fortnightly gravity exchange that supplies nutrients to surface waters that enhance biological production when nutrients would otherwise be limiting. This exchange delivers nutrients at least as far inland as the head station, while nutrients associated with an eddy near the mouth may be the cause of even higher productivity there. We discuss the impact of these nutrient sources to Saanich Inlet on the records of paleoproduction generated from two Ocean Drilling Program cores extracted from this fjord, and suggest that the fortnightly exchange buffers variations in nutrient supply occurring on sub-decadal or decadal scales.     

南京玄武湖蓝藻水华治理后水质和浮游植物的动态变化

玄武湖是典型的城市富营养化湖泊,2005年夏季暴发了大面积微囊藻水华,其后以粘土法为主,对微囊藻水华进行了应急治理。为了解应急治理后玄武湖水生态状况的变化,通过分析治理后浮游植物种类和数量变化以及重要理化指标的变化,探讨应急治理对湖水水质和浮游植物群落的影响。通过对比治理前和水华暴发期的监测数据,发现治理后浮游植物数量减少,种类增多;湖水总磷和叶绿素a的浓度都明显降低;水体透明度大幅提高,湖水总氮浓度随浮游植物的密度和菹草的生长而出现波动。     

基于Aquatox模型的洱海营养物投入响应关系模拟

针对洱海富营养化加剧以及蓝藻水华问题,应用Aquatox模型对洱海水环境进行模拟,确立了一套适用于洱海生态系统的特征参数,并将模拟结果与实测数据进行验证.验证结果表明模型较好地模拟了常规水质和藻类演替变化,与实际水环境状况大体吻合.以此为基础选取TN、TP和Chl.a指标对洱海营养物与富营养化状态的投入响应关系进行模拟研究.结果表明,洱海对于外界营养物输入比较敏感,对氮磷输入增减反应明显;外界氮磷的削减都对Chl.a含量有降低作用,TN的作用更加明显;氮磷的增加对于Chl.a含量都略有提升;同时调控氮磷具有协同作用,对Chl.a含量影响效果最明显;当水体TN浓度在0.34 mg/L的阈值以下水平,即洱海外源TN输入量削减比例达到43.3%以上时,藻类优势种由蓝藻变为硅藻,水体Chl.a含量大幅降低,有效抑制富营养化进程.     

A Sediment Quality Triad: Measures of sediment contamination,toxicity and infaunal community composition in Puget Sound

Increasing emphasis is being placed upon chemical analyses of sediments to determine the distribution and concentration of toxic chemicals in marine and aquatic environments. The resulting data are often used to characterize chemical accumulations, including delineation of ‘hotspots’. These data alone, however, provide no information regarding the possible biological significance of these accumulations. Direct biological testing is needed. the use of a Sediment Quality Triad (chemical, bioassay and infauna) of measurements is advocated here by the authors. The purpose of this study was to determine the correspondence among measures of the three components of the Triad, using available data from several studies of Puget Sound. Good overall correspondence among the three components of the Triad was observed, based upon a comparison of average values from urban and rural portions of the Sound. However, based upon comparisons of data on a station-by-station basis the chemical data alone were not always reliable indicators (and, therefore, predictors) of biological effects. Hence, the importance and usefulness of the Triad was substantiated.     

Dynamics and sources of dissolved organic carbon during phytoplankton bloom in hypereutrophic Lake Taihu (China)

To establish the influence of phytoplankton blooms on the dynamics and sources of dissolved organic carbon (DOC) in Lake Taihu, the concentrations and stable carbon isotope values (δ¹³C) of DOC and particulate organic carbon (POC) were analyzed, along with environmental factors, including water temperature, chlorophyll a (Chl a) concentration, phytoplankton community and total bacterial abundance, from March to August 2013 at five sites in Lake Taihu. Significant differences were observed in the DOC concentrations and δ¹³C_DOC values at the sampling sites. On average, the proportion of DOC in the total organic carbon (TOC) pool ranged from 30% ± 10% to 81% ± 7%. POC was positively associated with both Chl a concentration and cyanobacteria biomass, suggesting that cyanobacteria blooms contribute to the POC pool in Lake Taihu. Depleted ¹³C in DOC relative to POC was observed in August, indicating that DOC was partially derived from POC in August. However, Chl a explained only 40% of the variation in DOC in the entirety of Lake Taihu, and at two sites far from the estuary, the contribution of allochthonous carbon was less than 50% in August. These results suggested a greater influence of allochthonous sources on the DOC pool. Moreover, the biodegradability of DOC was further determined by the total dissolved carbohydrates to DOC ratio (TCHO/DOC), specific UV absorbance (SUVA₂₅₄), and the concentrations of bioavailable DOC (BDOC). On average, 17% of the variation in DOC was attributable to the BDOC pool, and the BDOC concentration correlated positively with Chl a, cyanobacteria biomass, and total bacterial abundance, suggesting that cyanobacteria–derived DOC is biodegradable and is preferentially utilized by bacteria.     

Marine species mortality in derelict fishing nets in Puget Sound, WA and the cost/benefits of derelict net removal

Derelict fishing gear persists for decades and impacts marine species and underwater habitats. Agencies and organizations are removing significant amounts of derelict gear from marine waters in the United States. Using data collected from repeated survey dives on derelict gillnets in Puget Sound, Washington, we estimated the daily catch rate of a given derelict gillnet, and developed a model to predict expected total mortality caused by a given net based on entanglement data collected upon its removal. We also generated a cost:benefit ratio for derelict gear removal utilizing known true costs compared to known market values of the resources benefiting from derelict gear removal. For one study net, we calculated 4368 crab entangled during the impact lifetime of the net, at a loss of $19,656 of Dungeness crab to the commercial fishery, compared to $1358 in costs to remove a given gillnet, yielding a cost:benefit ratio of 1:14.5.     

Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia

We investigated the effect of acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (Howe Sound, BC, Canada) on primary productivity and chlorophyll a levels in the receiving waters of Howe Sound before, during, and after freshet from the Squamish River. Elevated concentrations of copper (integrated average through the water column >0.050 mg l⁻¹) in nearshore waters indicated that under some conditions a small gyre near the mouth of Britannia Creek may have retained the AMD from Britannia Creek and from a 30-m deep water outfall close to shore. Regression and correlation analyses indicated that copper negatively affected primary productivity during April (pre-freshet) and November (post-freshet). Negative effects of copper on primary productivity were not supported statistically for July (freshet), possibly because of additional effects such as turbidity from the Squamish River. Depth-integrated average and surface chlorophyll a were correlated to copper concentrations in April. During this short study we demonstrated that copper concentrations from the AMD discharge can negatively affect both primary productivity and the standing stock of primary producers in Howe Sound.     

Missing role of groundwater in water and nutrient cycles in the shallow eutrophic lake Kasumigaura,Japan

A process‐based model was developed, NICE‐LAKE (NIES (National Institute for Environmental Studies) Integrated Catchment‐based Ecohydrology), which includes interactions between surface water, canopy, unsaturated water, aquifer, lake and rivers, and used it to model the shallow eutrophic Lake Kasumigaura in Japan. By estimating the spatial distribution of the hydrological cycle, the model shows that groundwater withdrawal greatly affects groundwater distribution and seepage and indirectly influences lake water level. The simulated seepage agrees excellently with the budget‐derived value calculated from the observed groundwater level, lake level and isotope analyses. The model showed that groundwater seepage and groundwater concentrations are important contributors to the eutrophication of Lake Kasumigaura, an important contribution not recognized in previous studies of the lake. Groundwater entering the lake from the north side is contaminated with high concentrations of nitrate and ammonia from intensive pig and cattle raising and cultivated fields. The simulation showed that this high nitrogen load plays an important role in the eutrophication of the lake (the nitrogen load in inflowing groundwater is 30% of river inflow and 4 times that from wastewater treatment plants) in spite of government policies to prevent overland flow of nutrients into the lake. Our results show that NICE‐LAKE is a powerful tool for forecasting how the water quality of the lake will be affected by the (illegal) disposal of animal excreta in the surrounding open fields. Copyright © 2007 John Wiley & Sons, Ltd.     

Estimation of mass and energy balance of glaciers using a distributed energy balance model over the Chandra river basin (Western Himalaya)

The ongoing glacier shrinking in the Himalayan region causes a significant threat to freshwater sustainability and associated future runoff. However, data on the spatial climatic contribution of glacier retreat is scanty in this region. To investigate the spatially distributed glacier surface energy and mass fluxes, a two-dimensional mass balance model was developed and applied to the selected glaciers of the Chandra basin, in the Upper Indus Basin, Western Himalaya. This model is driven by the remote sensing data and meteorological variables measured in the vicinity of the Chandra basin for six hydrological years (October 2013 to September 2019). The modelled variables were calibrated/validated with the in-situ observation from the Himansh station in the Chandra basin. We have derived air temperature (T_a ) spatially using the multivariate statistical approach, which indicates a relative error of 0.02–0.05°C with the observed data. Additionally, the relative error between the modelled and observed radiation fluxes was <10.0 W m⁻². Our study revealed that the Chandra basin glaciers have been losing its mass with a mean annual mass balance of −0.59 ± 0.12 m w.e. a⁻¹ for the six hydrological years. Results illustrated that the mean surface melt rate of the selected glaciers ranged from −5.1 to −2.5 m w.e. a⁻¹ that lies between 4500 and 5000 m a.s.l. The study revealed that the net radiation (R_N) contributes ~75% in total energy (F_M ) during the melt season while sensible heat (H_S) , latent heat (H_l) , and ground heat (H_G) fluxes shared 15%, 8%, and 2%, respectively. Sensitivity analysis of the energy balance components suggested that the mass balance is highly sensitive to albedo and surface radiations in the study area. Overall, the proposed model performed well for glacier-wide energy and mass balance estimation and confirms the utility of remote sensing data, which may help in reducing data scarcity in the upper reaches of the Himalayan region.     

Simulating daily, monthly and annual water balances in a land surface model using alternative root water uptake schemes

Hydrological simulations at multi-temporal time scales by a widely used land surface model (LSM) are investigated under contrasting vegetation and meteorological conditions. Our investigation focuses particularly on the effects of two different representations of root water uptake and root profile on simulated evapotranspiration (ET) and soil moisture by the Integrated BIosphere Simulator (IBIS). For this purpose, multi-year eddy covariance measurements, collected at four flux-tower sites across North America, were used to gauge IBIS simulations with: (a) its standard version (IBIS2.1), in which static root water uptake (RWU) and root profile schemes are incorporated; and (b) a modified version in which dynamic RWU and root profile schemes replaces the static schemes used in the standard version. Overall, our results suggest that the modified version of the model performs more realistically than the standard version, particularly when high atmospheric demand for evaporation is combined with high atmospheric vapour pressure deficit and low soil water availability. The overall correlation between simulated and measured monthly ET rates at the simulated sites reached 0.87 and 0.91 for the standard and the modified versions, respectively. Our results also show that the incorporation of the dynamic RWU in IBIS yields improved simulations of ET under very dry conditions, when soil moisture falls down to very low levels. This suggests that adequate representations of vegetation responses to drought are needed in LSMs as many state of the art climate models projections of future climate indicate more frequent and/or more intense drought events occurring in some regions of the globe. Our analysis also highlighted the urgent need for adequate methodologies to correct field measurements that exhibit energy imbalances in order to provide rigorous assessments of land surface model simulations of heat and mass exchanges between the land surface and the atmosphere.     

Effusion rate and energy balance of Paricutin eruption (1943–1952), Michoacan, Mexico

The annual effusion rate of the Paricutin eruption shows an exponential decrease with time. This trend was observed during eruptions in other volcanoes and is explained by a simple model of the temporal changes of effusion rate proposed by Machado (1974). The regular trend of the effusion rate permits, in this case, a forecast of the length of the eruption. The energy balance of the eruption shows that part of the available energy was absorbed in a process of differentiation of the magma and this fact probably shortened the eruption.     

抚仙湖、洱海、滇池浮游藻类功能群1960s以来演变特征

作为主要的初级生产者,浮游植物在水生生态系统中扮演着重要的角色,浮游植物的时空分布反映了生态环境的变化.依据浮游植物的形态、生理、生态特点而定义的浮游藻类功能群对藻类的耐受性和敏感性进行了描述,因而浮游藻类功能群的组成是生境特征的良好指示者.对1960s至今抚仙湖、洱海、滇池3个高原湖泊的浮游藻类组成进行分析,并首次将功能群理论运用到这3个湖泊.结果表明,3个湖泊的浮游藻类优势功能群组成在近50～60年间发生了明显的改变:抚仙湖的浮游藻类优势功能群演变过程为C、X2、Lo、F、P(1960s)-H1、C、P(1980s)-P、C、T(1990s)-T(2000年以后);洱海的浮游藻类优势功能群演变过程为J、Lo、MP、C、H1(1960s)-C、H1(1980s)-C、H1(1990s)-C、H1、M(2000年以后);滇池的浮游藻类优势功能群演变过程为J、N、P、MP、Lo(1960s)-J、P、MP、M(1980s)-J、M(1990s)-M(2000年以后).抚仙湖、洱海、滇池水体内的藻类功能群演替趋势特征,即耐低温物种的减少以及喜营养物种的增加,表明3个高原湖泊在近几十年可能受到了气候变暖和营养程度增加的影响.     

Evaluation of uncalibrated energy balance model (BAITSSS) for estimating evapotranspiration in a semiarid,advective climate

The backward‐averaged iterative two‐source surface temperature and energy balance solution (BAITSSS) model was developed to calculate evapotranspiration (ET) at point to regional scales. The BAITSSS model is driven by micrometeorological data and vegetation indices and simulates the water and energy balance of the soil and canopy sources separately, using the Jarvis model to calculate canopy resistance. The BAITSSS model has undergone limited testing in Idaho, United States. We conducted a blind test of the BAITSSS model without prior calibration for ET against weighing lysimeter measurements, net radiation, and surface temperature of drought‐tolerant corn (Zea mays L. cv. PIO 1151) in a semiarid, advective climate (Bushland, Texas, United States) in 2016. Later in the season (20 days), BAITSSS consistently overestimated ET by up to 3 mm d^?1. For the entire growing season (127 days), simulated versus measured ET resulted in a 7% error in cumulative ET, RMSE = 0.13 mm h^?1, and 1.70 mm d^?1; r² = 0.66 (daily) and r² = 0.84 (hourly); MAE = 0.08 mm h^?1 and 1.24 mm d^?1; and MBE = 0.02 mm h^?1 and 0.58 mm d^?1. The results were comparable with thermally driven instantaneous ET models that required some calibration. Next, the initial soil water boundary condition was reduced, and model revisions were made to resistance terms related to incomplete cover and assumption of canopy senescence. The revisions reduced discrepancies between measured and modelled ET resulting in <1% error in cumulative ET, RMSE = 0.1 mm h^?1, and 1.09 mm d^?1; r² = 0.86 (daily) and r² = 0.90 (hourly); MAE = 0.06 mm h^?1 and 0.79 mm d^?1; and MBE = 0.0 mm h^?1 and 0.17 mm d^?1 and generally mitigated the previous overestimation. The advancement in ET modelling with BAITSSS assists to minimize uncertainties in crop ET modelling in a time series.     

Assessing impacts of riparian buffer zones on sediment and nutrient loadings into streams at watershed scale using an integrated REMM‐SWAT model

Riparian buffer zones in agriculture dominated watersheds play important roles in reducing nonpoint source pollution into aquatic ecosystems and are widely used as a Best Management Practice. Assessment of the effectiveness of riparian buffer zones by modeling method is widely used for watershed management as field measurement‐based assessment is difficult and expensive. The integration of Riparian Ecosystem Management Model (REMM) and Soil and Water Assessment Tool (SWAT) has been developed to simulate the effect of nonpoint source pollution reduction by riparian buffer zones at subbasin scale. However, there are problems in using the integrated model at subbasin scale, as the size of subbasin partition could affect the pollutant reduction rate by riparian buffers. In this study, we partitioned a large watershed with size of 1331 ha into sub‐watersheds with sizes of 666, 333, 166, 83, 51, and 29 ha, and then compared the different simulation results. We found that the modeling could yield more convergent results when the sub‐watersheds were partitioned into suitable size. In the studied area, the suitable sub‐watershed size was less than about 166 ha for runoff and nitrogen and 83 ha for sediment and phosphorus. Among the eight sub‐watersheds (partitioned based on the size of 166 ha), results showed that the effects of riparian buffers on runoff and nutrient loading varied drastically. The reduction rate varied from 0.26% to 30.13% for runoff, 29.4% to 74.07% for sediment, 9.61% to 57.85% for nitrogen, and 18.61% to 68.12% for phosphorus, respectively.