非稳沉采煤沉陷区沉积物-水体界面的氮、磷分布及迁移转化特征

以淮南后湖非稳沉采煤沉陷区沉积物-水体界面为研究对象,分析该湖未开发区(A区)、水产养殖区(B区)和水生蔬菜种植区(C区)3个功能区上覆水-间隙水-沉积物体系中氮、磷分布及其迁移特征.结果表明,氮、磷在不同水体界面的分布差异较大.其中上覆水中氮、磷浓度表现为A区B区C区;间隙水中氮、磷分布差异不显著,然而各功能区间隙水的氮、磷浓度明显高于上覆水,氮、磷主要由间隙水向上覆水中移动;沉积物中氮、磷含量以C区最高.后湖采煤沉陷区水体表现出氮污染、磷限制的现象.     

太湖藻型湖区沉积物中生物易降解物质组成及分布规律

为研究富营养化湖泊藻型湖区沉积物中生物易降解有机质的组成及其垂向分布特征,选取太湖竺山湾湖滨带和开敞湖区采集沉积物柱状样,利用微电极技术测定沉积物-水界面理化指标的剖面特征,并对沉积物中含水率、烧失量、色素含量、总有机碳、总氮以及生物易降解物质（总蛋白、总糖和总脂）进行测定.结果表明：藻型湖区沉积物-水界面处溶解氧、pH和氧化还原电位在垂向剖面上呈现出随深度增加而下降的趋势,空间上存在明显的异质性,湖滨带沉积物-水界面溶解氧、pH和氧化还原电位显著低于开敞湖区,而沉积物-水界面H₂S浓度在垂向上则表现为随深度先降低而后升高的趋势.此外,藻型湖区沉积物中生物易降解有机质的组成和分布同样存在明显的空间异质性.组成上以脂类（7.7 mg/g）为主,其次是糖类（4.5 mg/g）,蛋白质（0.8 mg/g）含量最低;空间上,湖滨带沉积物中生物易降解有机质含量显著高于开敞湖区,表层15 cm以上沉积物含水率和烧失量较高,有机质含量丰富.     

福建山仔水库不同季节表层沉积物内源磷负荷分析

对山仔水库沉积物各形态磷的季节性特征以及夏、冬季磷释放速率进行研究.结果表明,该水库表层沉积物含有较丰富的磷,4个季节各采样点表层沉积物总磷含量范围为(521.23±7.60)~(1255.54±11.03)μg/g,夏季各采样断面中总磷含量及各形态磷含量均高于其他季节.表层沉积物磷以无机磷为主,且主要赋存形态为铁/铝结合态磷.活性较大的铁/铝结合态磷和有机磷占总磷量的77%~90%.柱状样模拟实验结果表明:夏季溶解性磷释放平均速率范围在1.66~2.49 mg/(m2·d),冬季溶解性磷释放平均速率范围为0.69~1.29 mg/(m2·d),夏季各采样点表层沉积物磷释放速率约为冬季的2倍.由于水温分层,夏季沉积物释放的溶解性磷主要滞留在上覆层,但夏季暴雨天气可能导致水温分层破坏,沉积物释放的溶解性磷对水体将产生重要影响;冬季由于水温分层破坏导致上、下水层混合,沉积物释放的溶解性磷被带到上层,对上覆水体水质的影响不容忽视.     

不同密度藻屑堆积下沉积物碳氮磷释放特征

蓝藻碎屑分解引起氮磷释放已受到广泛关注,但堆积的藻屑与沉积物交互作用引发污染物释放的效应知之甚少.采集于桥水库沉积物柱状样,设置5个藻屑添加组和对照组(无藻屑添加),恒温培养(27±1℃),模拟夏季温度条件下不同密度藻屑堆积下沉积物中碳氮磷释放特征.结果表明:藻屑堆积后加强了上覆水中溶解氧与硝态氮的消耗,5个藻屑添加组18小时后上覆水均处于厌氧状态.各实验组上覆水中的溶解性有机碳(DOC)浓度在第3小时增加,且SUVA254值处于0.54~1.74 L/(mg·m)之间,说明DOC可能来源于藻源性释放.各藻屑添加组培养过程中上覆水的溶解性有机氮(DON)、铵态氮和正磷酸盐浓度持续增加,最高平均释放速率分别达4.44、0.20和0.03 mg/(L·h),分别为对照组的21.73、1.76和67.58倍;其中DON为溶解性总氮主要存在形态,在实验结束时DOC/DON比值降低,说明藻屑或者沉积物有机质短期内并未完全矿化,且DOC优先DON被微生物利用.因此蓝藻碎屑堆积增强了沉积物需氧量,加快沉积物与水之间的氮磷营养盐、DOC循环,从而对沉积物中污染物地球化学循环过程造成进一步的影响.     

太湖西北湖区浮游植物和无机、有机氮的时空分布特征

以太湖重度蓝藻水华发生的西北湖区为研究对象,从河口至湖心区设置5个采样点,于2012年10月至2013年10月逐月采集表层水体样品,测定了水温、溶解氧和浮游细菌丰度,并分析了浮游植物群落结构的组成、溶解性无机氮(DIN)和有机氮(DON)浓度以及氮磷比.研究结果表明,太湖西北湖区浮游植物主要由蓝藻、硅藻、绿藻和隐藻组成.可能由于风、浪等混合作用使太湖西北湖区不同采样点之间蓝藻细胞密度没有显著差异.蓝藻生物量在浮游植物中所占比例最高为34%±15%,春季部分点位隐藻生物量高于50%,表明隐藻与蓝藻的相互竞争趋势显著.CCA排序图结果表明,DIN、DON浓度以及总氮∶总磷比(TN∶TP比)是影响西北湖区浮游植物优势属分布的重要环境因子.5个采样点铵态氮(NH_4~+-N)与DIN浓度具有显著差异,与DON浓度没有显著差异.夏季蓝藻水华暴发期间,可能由于蓝藻的吸收利用引起NH_4~+-N和硝态氮(NO_3~--N)浓度迅速降低.此外,由于NH_4~+-N浓度还可能受到沉积物NH_4~+-N释放的影响,因此,蓝藻细胞密度与NO_3~--N的相关系数和显著水平均高于NH_4~+-N.夏季TN∶TP比和DIN∶TP比降至最低,表明该湖区浮游植物,尤其是蓝藻的生长可能受到氮限制.蓝藻细胞密度与DON浓度呈显著负相关,表明在氮限制条件下,DON可能是蓝藻氮素利用的重要补充.     

环境因子对五里湖沉积物磷释放的影响

本文论述了溶解氧、pH、温度和沉积物中微生物作用对太湖五里湖区沉积物磷释放的影响,以及在pH为8.4、好氧和厌氧二种状态下沉积物释放试验后滤液对斜生栅列藻(Scende es(?) obliq(?))和羊角月芽藻(Selena(?) ca(?))增长的影响.结果表明:溶解氧降低、pH和温度升高、微生物作用有利于沉积物磷向水体释放,与湖水组相比,厌氧状态下沉积物磷释放后滤液能显著促进斜生栅列藻增长,但不能促进羊角月芽藻增长,好氧状态下沉积物磷释放后滤液均不能促进二种藻类的增长。     

菹草、伊乐藻对沉积物磷形态及其上覆水水质的影响

采集武昌南湖湖水、沉积物进行沉水植物的盆栽试验,试验设置沉积物未施磷处理和施100mg/kg磷处理,分别对应沉积物低内源磷和高内源磷状态,同时种植菹草、伊乐藻,以研究沉积物中磷形态及上覆水水质的变化特点.研究从2007年9月15日开始,历时160d.结果表明,高内源磷沉积物处理后,上覆水中水溶性总磷含量在沉水植物的作用下明显降低;种植沉水植物可使水体总磷、总氮、叶绿素a含量显著降低,且伊乐藻对总磷的净化效果优于菹草;沉水植物对高内源磷沉积物的上覆水中叶绿素a的控制比对低内源磷条件下的效果更好;无论沉积物是否输入磷,在盆栽条件下,上覆水中叶绿素a随时间的变化均能较好地用一级动力学模型来描述;上覆水TDP、TP与沉积物中Ca_(10)-P之间有极显著正相关;种植菹草或伊乐藻的沉积物中Ca_(10)-P与上覆水中TDP和TP的相关系数分别为0.990(P≤0.01)和0.977(P≤0.05).     

长江中下游湖泊沉积物中磷的形态及藻类可利用量

调研了长江中下游地区25个浅水湖泊的35个样点表层沉积物中磷的地球化学形态特征,以及太湖沉积物中藻类可利用磷(AAP)的空间分布,垂向分布特征及其蓄积量,探讨了浅水湖泊表层沉积物中磷的赋存量,地球化学形态及其与水草,湖水磷浓度,叶绿素(Chl-a)浓度之间的关系.结果表明,长江中下游地区浅水湖泊的表层沉积物中可交换态磷(Ex-P)含量与水体总磷(TP),溶解性总磷(DTP)及溶解性反应活性磷(SRP)浓度关系密切,有水草湖区的沉积物中生物易利用磷(Bio-P)含量显著低于无水草湖区及藻型湖区.太湖梅梁湾沉积物泥芯中,表层3 cm沉积物中Ex-P含量显著增高,而夏季还原条件下容易转变为溶解态磷的铁磷(Fe-P)含量峰值则出现在4～10cm深度.太湖表层沉积物的Bio-P含量与夏季叶绿素浓度密切相关,说明表层沉积物的Bio-P及AAP可以作为沉积物内源释放风险的指示参数.太湖表层1 cm底泥中所含有的AAP量估计多达268.6吨,风浪扰动能将大量的AAP带入水体,对太湖蓝藻水华暴发起着不可忽视的作用.     

山东省东平湖菹草(Potamogeton crispus)腐烂过程中水体温室气体溶存浓度及扩散通量变化

为了解东平湖菹草(Potamogeton crispus)腐烂分解对水体温室气体溶存浓度和界面扩散通量的影响,于2016年5-7月在东平湖菹草腐烂期采集上覆水和沉积物柱样,测定上覆水和孔隙水中温室气体(N_2O、CH_4和CO_2)的溶存浓度,采用Fick第一定律和双层模型计算沉积物-水-气界面扩散通量,同时分析上覆水和沉积物的理化性质,并采用网袋分解法于现场进行菹草腐烂分解试验,以探究东平湖菹草腐烂过程中温室气体溶存和扩散的主要影响因子及其主要来源.结果表明,菹草腐烂符合二次指数模型,分为快速衰减和慢速分解两个阶段;菹草腐烂过程中上覆水pH和亚硝态氮浓度表现为先降低后升高,而溶解氧、氨氮、硝态氮和可溶性正磷酸盐浓度则为先升高后下降,沉积物中铵态氮含量表现为先升高后降低,硝态氮为先降低后显著升高,有机质和p H呈降低-升高-降低的波动变化;上覆水中各温室气体浓度和水气界面扩散通量均表现为CO_2 CH_4 N_2O,其扩散通量分别为5862.9±5441.4、31.15±41.3和0.15±0.57μmol/(m~2·h),整体表现为大气温室气体的"源",并以碳排放为主;上覆水中N_2O浓度和水-气界面扩散通量均先降低后升高,孔隙水中N_2O浓度在快速和慢速分解阶段分别出现极大值(22.7和55.6 nmol/L),而其沉积物-水界面通量前期持续增加至腐烂结束后迅速降低;上覆水和孔隙水中CH_4浓度及其各界面通量均表现为前期略有降低后持续升高;上覆水中CO_2浓度和水-气界面通量表现为持续升高后降低并趋于稳定,而孔隙水中CO_2呈波动变化,在菹草腐烂初期向孔隙水扩散,后期向上覆水扩散.水温是影响上覆水中温室气体浓度和水-气界面通量的主要因素;沉积物是水体N_2O和CH_4的主要来源,孔隙水中浓度是控制其沉积物-水界面扩散的重要因素;而上覆水中CO_2呈现多源性,但以上覆水中有机物质的矿化为主.     

过氧化钙在处理厌氧底泥中的应用初探

为改善河道厌氧底质及内源氮、磷等营养盐释放问题,考察对沉水植被恢复的影响,研发可同步解决沉积物供氧和削减内源氮、磷释放的氧缓释材料.实验通过向沉积物-水界面处散点注射不同剂量的过氧化钙(Ca O2),研究界面处溶解氧的动态变化特征及表层沉积物与底层水体之间溶解态氮、磷的交换过程.结果表明:添加Ca O2显著提高了界面处底层上覆水溶解氧浓度,随着Ca O2浓度的增加溶解氧浓度增加,不同处理组之间具有显著差异;Ca O2对沉积物中PO3-4-P释放具有明显的抑制作用,且随Ca O2浓度的增加抑制效果愈加明显,上覆水中可溶性活性磷浓度最大可削减98%.实验开始时,磷释放速率可降至-241.916±22.501 mg/(m2·d),降幅最高可达到144%;Ca O2对沉积物NH+4-N释放的抑制效果不佳,上覆水中NH+4-N浓度随着时间的变化波动性较大,且有逐渐增大的趋势.另外,添加Ca O2会显著提高底层上覆水p H值,不同处理组之间差异显著,但当Ca O2投加量小于0.529 kg/m2时,不会对苦草种子的萌发生长有显著影响,p H值波动在可接受范围内(7.62~10.87).因此,结合污染沉积物的状况,适当地投加Ca O2有望同步解决底质厌氧、内源磷释放及后期沉水植被定植底质生境改善的问题,可推荐为一种黑臭污染底泥治理技术在实际的河道生态工程中应用,其适宜浓度为0.176 kg/m2左右.     

滆湖水体光学性质初步研究

基于2009年7月至2010年6月滆湖全湖15个采样点的水体光学参数及相关水质理化因子数据,分析滆湖水体周年光合有效辐射(PAR)衰减特性,以期为滆湖沉水植物生态修复提供相关水体光学资料.结果表明,滆湖水体PAR衰减系数(Kd)周年变化范围为1.32～17.42 m-1.秋季Kd相对最小,平均值为2.35 m-1,变化范围为1.32 ～3.70 m-1;夏季Kd相对最大,平均值为6.23 m-1,变化范围为3.68～17.42 m-1.春、秋、冬季,滆湖水体真光层平均深度均满足沉水植物的生长需求,而在夏季滆湖水体真光层平均深度仅为0.84m,小于全湖平均水深(1.20 m),因此夏季PAR是限制沉水植物恢复的因子之一.滆湖水体Kd与透明度(SD)在秋、冬季的关系为:Kd =2.089 +0.705/SD.叶绿素a浓度和悬浮物浓度是影响滆湖水体Kd的重要因子之一.     

Phosphate uptake in a macrophyte-rich Pampean stream

We estimated phosphate uptake in an eutrophic and macrophyte-rich Pampean stream, in a basin where dominant land use was agricultural activity. Our hypothesis was that phosphate retention may be linked to macrophyte abundance, especially that of submerged plants. Four short-term constant-rate phosphate addition experiments were carried out in late spring, summer, autumn and winter under different discharge, background phosphate concentration and macrophyte abundance. Changes in added soluble reactive phosphorus (SRP) concentration were monitored along the studied reach and corrected for dilution to estimate phosphate uptake length (S_w) and other spiraling metrics (V_f or mass transfer coefficient, and U or nutrient uptake rate). All spiraling metrics indicated a higher SRP retention in spring than in autumn, despite macrophyte cover was similar in both sampling dates (39% and 51%, respectively). Phosphate retention was not detected neither in summer (when macrophyte biomass and especially that of submerged plants was the highest one) nor in winter. Ambient SRP concentrations in the stream were an order of magnitude higher than concentrations observed in pristine streams; nevertheless, under the varying conditions of discharge and phosphate levels observed in our study, we found no retention in summer and winter, a phosphate uptake comparable with those measured in impaired streams in autumn, and with those measured in pristine streams in late spring.     

呼伦湖浮游植物群落季节动态及其与环境因子的关系

为探究呼伦湖浮游植物群落的季节变化特征及其与环境因子的关系,本研究分别于2019年3、5 10月对呼伦湖浮游植物的种类、细胞密度和生物量及湖水水质进行调查.结果显示,共鉴定出120种浮游植物,隶属于7门72属.从浮游植物群落季节组成差异上来看,春季绿藻门种类数最多,其次是硅藻门、蓝藻门;夏秋季绿藻门种类数最多,蓝藻门次之;冬季硅藻门种类数最多,绿藻门次之.呼伦湖浮游植物优势种主要为硅藻门的梅尼小环藻(Cyclotella meneghiniana)、蓝藻门的卷曲长孢藻(Anabaena circinalis)和细小平裂藻(Merismopedia minima),种类数在春季最多,秋冬季最少.浮游植物细胞密度在春季(123.52×10⁴cells/L)和冬季(16.41×10⁴cells/L)较夏季(280.80×10⁴cells/L)和秋季(380.63×10⁴cells/L)低,春冬季绿藻门细胞密度最高,夏秋季蓝藻门细胞密度最高.就浮游植物生物量而言,夏季(0.38mg/L)最大,其次是秋季(0...     

Seasonal contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system (Ría de Vigo, NW Spain)

The aim of this study is to explore the contribution of living phytoplankton carbon to vertical fluxes in a coastal upwelling system as a key piece to understand the coupling between primary production in the photic layer and the transfer mechanisms of the organic material from the photic zone. Between April 2004 and January 2005, five campaigns were carried out in the Ría de Vigo (NW Iberian Peninsula) covering the most representative oceanographic conditions for this region. Measurements of particulate organic carbon (POC), chlorophyll-a (chl a), phaeopigments (phaeo), and identification of phytoplankton species were performed on the water column samples and on the organic material collected in sediment traps.The POC fluxes measured by the sediment traps presented no seasonal variation along the studied period ranging around a mean annual value of 1085±365 mg m⁻² d⁻¹, in the upper range of the previously reported values for other coastal systems. The fact that higher POC fluxes were registered during autumn and winter, when primary production rates were at their minimum levels points to a dominant contribution of organic carbon from resuspended sediments on the trap collected material. On the contrary, fluxes of living phytoplankton carbon (C_phyto) and chl a clearly presented a seasonal trend with maximum values during summer upwelling (546 mg m⁻² d⁻¹ and 22 mg chl a m⁻² d⁻¹, respectively) and minimum values during winter (22 mg m⁻² d⁻¹ and 0.1 mg chl a m⁻² d⁻¹, respectively). The contribution of C_phyto to the vertical flux of POC ranged between 2% and 49% in response to the pelagic phytoplankton community structure. Higher values of C_phyto fluxes were registered under upwelling conditions which favour the dominance of large chain-forming diatoms (Asterionellopsis glacialis and Detonula pumila) that were rapidly transferred to the sediments. By contrast, C_phyto fluxes decreased during the summer stratification associated with a pelagic phytoplankton community dominated by single-cell diatoms and flagellates. Minimal C_phyto fluxes were observed during the winter mixing conditions, when the presence of the benthic specie Paralia sulcata in the water column also points toward strong sediment resuspension.     

丹江口水库浮游植物群落时空变化及其与环境因子的关系

研究丹江口水库在完成高水位蓄水期间浮游植物群落的时空动态特征可为丹江口水库的水质保护与生态系统结构优化及健康管理提供一定科学依据。本研究基于2018—2020年的水库浮游植物监测数据,结合同期水库水体的理化参数,分析了丹江口水库浮游植物在不同年度、季度及空间的变化特征,以及影响浮游植物群落结构变化的主要环境因子。结果显示该区域共检测出浮游植物7个门类,其中蓝藻门、硅藻门、绿藻门、隐藻门为优势类群。2018—2020年浮游植物年均密度分别为1.96×10⁶、2.55×10⁶和5.07×10⁶ cells/L,呈现出逐年增高趋势。浮游植物季度密度表现为秋季>夏季>春季>冬季,在夏秋季节蓝藻门和绿藻门占优势,春冬季节硅藻门和隐藻门占优势,同时硅藻门在四季中均占据生长优势。空间上库区浮游植物密度明显高于支流,且汉江库区浮游植物密度高于丹江库区,其中蓝藻门和绿藻门主要在库区大量出现,而支流则以硅藻门和隐藻门为主。RDA分析显示,影响丹江口水库浮游植物的主要环境因子是水温,其次为化学需氧量、氨氮和总磷。在不同季节和...     

大型水生植物—藻类混合型富营养湖泊的生态管理模式——以固城湖为例

Lake Gucheng is located in the southeast of Nanjing, with an area of 24.3 km², an average depth of 2 meters. The macrophytes of the lake were used to be abundant and their biomass was about 4.96 mg·m^-2. The annual average contents of total phosphorus (TP), total nitrogen (TN), PO^3- -P, COD_Mn and BOD₅ 0.03, 1.31, 0.005, 3.61 and 1.46 mg·L^-1, respectively. Thus, the water quality of this lake is quite well. Recently, the water quality in pari of the lake became worse because of some unreasonable exploitation and utilization of bioresources. The interactions between phytoplankton (N₁), macrophyte (N₂), fish (N₃), crab (N₄) were studied here. The macrophyte has great influences on both phytoplanktons, fish and crab, controlling the water quality and maintaining the fishery productivity. On the other hand, the phytoplankton, fish and crab also influence the macrophyte. It is key method of ecological management to maintain the macrophyte by fishery culture. Therefore, a modified Lotka-Volterra model has been established to estimate the interaction between N₁, N₂, N₃, N₄ and the influences of some water environmental parameters on these aquatic organism, environmental and economic effect. The main model consists four compart-mental models and four submodels, involved 12 external variables, 8 state variables, 19 universal constants and 11 parameters. The values of most parameters were found from our experiments and calibrated by the model and actually measured data. The model has been validated by comparison the computed and experimental data of phytoplankton and macrophyte. The theoretical outputs showed a good agreement with the measured data. This model predicated that if the standing crop offish and crab was higher than 2.65 ·m^-2 during springtime in this lake, macrophytes would not grow, chlorophyll a content would arrive 34.8 mg·m^-3 and the water quality would decrease. If the macrophyte grow well, the maximum fishery productivity would be about 1 600 t. In this case, the annually averaged phytoplankton chlorophyll a content should be 3.69 mg·m^-3, which is lower than the criterion (10 mg·m^-3) for eutrophic state. From 1991 to 1996, Lake Gucheng was managed with this model, its water quality maintain quite well, chlorophyll a content decreased from 3.51 (1991) to 1.89 mg·m^-3 (1994). Meanwhile, the fishery productivity increased and the economic effect heightened year by year.     

引水工程絮凝剂余铝对杭州西湖水体、底泥铝盐分布的影响

通过对杭州西湖综合保护工程钱塘江引水范围内多个湖区水体和底泥中铝盐含量的调查分析,研究了工程絮凝剂余铝对西湖水体、底泥铝盐及沉水植物附着物的影响.结果表明:(1)引水工程输入的絮凝剂残余铝盐导致各湖区入水口水中铝离子含量普遍高于湖心,高出7.86%~288.55%不等,但底泥中Al_2O_3含量在整个湖区分布较为均匀;(2)约0.04~0.20 m/s流速下,沉水植物很容易成为残余铝盐絮凝物的附着受体;(3)秋、冬季水体中铝离子浓度较高,对西湖水生生物存在更大的生物潜在危害,有必要重视秋、冬季的沉水植物恢复工作.引水工程对西湖水体的影响是长久且难以预见的,在引水的同时应尽量减少其负面影响,可减少絮凝剂的使用或选择环保型絮凝剂,并选择合适的水生植物.     

五里湖富营养化过程中水生生物及生态环境的演变

五里湖是太湖西北部一个小型浅水湖湾,是无锡市的饮用水源和主要风景游览区。50年代时,该湖基本保持着原始状态,全湖以大型水生植物占优势。湖水清澈见底,水质为中营养水平,溶氧接近饱和,对外来的N、P污染冲击具有很强的缓冲能力。底泥的氧化程度较高,磷和有机物含量仅为0.023％和0.75％。浮游藻类受到了大型水生植物的强烈抑制,年均数量为26.7×10~4个/L,以硅藻和隐藻为主;从春季至秋季,随着大型水生植物的增长,浮游藻类数量大幅度减少。浮游动物多达190种,年均数量为5660ind./L。大型底栖动物较多,以日本沼虾和螺、蚌类为主。鱼类资源十分丰富,63种鱼中以凶猛性鱼类占优势,并有较多的底栖性鱼类。 自50年代以来,大约有1/2的湖面被围垦,沿岸带生态条件被破坏,失去了最适合于大型水生植物生长的浅水区。加之60年代后期在全湖放养草鱼,水生植被遭到彻底毁灭。外源污染加剧,引起了水质的严重富营养化。围垦和修建水闸隔断了五里湖与太湖间的通道,限制了两个水体间的水流交换,妨碍了污染物的稀释扩散,使得来自无锡市区的污水成了五里湖的主要补给水源,加速了富营养化的进程。五里湖水质已达重富营养水平,透明度小于0.5m,缺氧较为严重。营养物在底泥中大量积累,TP和TOC含量分别增高了4.17倍和1.87倍。在春末     

Carbonate sedimentation in seagrass beds on Ishigaki‐jima,Ryukyu Islands,southwestern Japan

In order to investigate biota and sedimentary facies, and to delineate processes of carbonate sedimentation in seagrass beds, we conducted sedimentological investigations along three onshore–offshore transects at two sites (Nagura and Yoshihara) on Ishigaki‐jima, Ryukyu Islands. Along the transects, the seagrass beds extended seaward 20–40 m from shore, and their widths parallel to the shore ranged from 60 to >110 m. The seagrass was dominated by Thalassia hemprichii, Cymodocea rotundata and subordinate C. serrulata. Seasonal changes in seagrass coverage were evident, with mean coverage relatively higher in summer and fall (July and October) than in winter and spring (January and April). The surface sediment throughout the seagrass beds was dominated by medium to very coarse sand‐sized bioclasts displaying grainstone/packstone fabrics. Bioclasts were dominated by corals and coralline algae, with lesser benthic foraminifers, mollusks, echinoids, and Halimeda. The grainstone/packstone was underlain by gravelly sediment with coral clasts, showing a rudstone fabric, at the Nagura Site. The lower part of the core sediment was blackened, indicating a reducing environment. Two dates of corals collected at the Nagura and Yoshihara sites (24.5 cm and 16.5 cm below the sea bottom) were 2781–2306 and 4374–3805 cal BP (2σ age range), respectively, suggesting extremely low sedimentation rates (<0.1 mm/year). Sediment influx was higher during July–January than during January–July. The relatively large influx during summer and fall is caused by massive sediment transport during typhoons and storms. The total sediment influx (i.e., suspension‐load sediment transportation) is 74–96 kg CaCO₃/m²/year at the Nagura Site and 21–57 kg CaCO₃/m²/year at the Yoshihara Site. Sediment influx was significantly greater in the seagrass beds than in surrounding areas, providing supporting evidence for an sediment trapping function of seagrass beds. Our data indicate that seagrass beds in the Ryukyu Islands are characterized by high sediment fluxes and extremely low sedimentation rates.