The structure of phytoplankton communities in the eastern part of the Laptev Sea

Studies have been performed on a transect along 130°30′ E from the Lena River delta (71°60′ N) to the continental slope and adjacent deepwater area (78°22′ N) of the Laptev Sea in September 2015. The structure of phytoplankton communities has distinct latitudinal zoning. The southern part of the shelf (southward of 73°10′ N), the most desalinated by riverine discharge, houses a phytoplankton community with a biomass of 175–840 mg/m², domination of freshwater Aulacoseira diatoms, and significant contribution of green algae (both in abundance and biomass). The northern border for the distribution range of the southern complex of phytoplankton species lies between the 8 and 18 psu isohalines (~73°10′ N). The continental slope and deepwater areas of the Laptev Sea (north of 77°30′ N), with a salinity of >27 psu in the upper mixed layer, are populated by the community prevalently composed of Chaetoceros and Rhizosolenia diatoms, very abundant in the Arctic, and dinoflagellates. The phytoplankton number in this area fall in the range of 430–1100 × 10⁶ cell/m², and the biomass, in the range of 3600 mg/m². A moderate desalinating impact of the Lena River discharge is observed in the outer shelf area between 73°20′ and 77°30′ N; the salinity in the upper mixed layer is 18–24 psu. The phytocenosis in this area has a mosaic spatial structure with between-station variation in the shares of different alga groups in the community, cell number of 117–1200 × 10⁶ cells/m², and a biomass of 1600–3600 mg/m². As is shown, local inflow of “fresh” nutrients to the euphotic layer in the fall season leads to mass growth of diatoms.     

Effects of salinity, temperature and food type on the uptake and elimination rates of cd, cr, and zn in the asiatic clamcorbicula fluminea

Laboratory radiotracer experiments were conducted to determine assimilation efficiencies (AE) from ingested algal food and oxic sediment particles, uptake rates from the dissolved phase, and the efflux rates of Cd, Cr and Zn in the Asiatic clamCorbicula fluminea. Among three elements, AE from both algal and sediment food was greatest for Cd, followed by Zn and Cr. The AEs of tested elements from algal food(Phaeodactylum tricornutum) were consistently higher than those from sediments at a given salinity and temperature. The influence of salinity (0, 4 and 8 psu) and temperature (5, 13 and 21¼) on the metal AEs was not evident for most tested elements, except Cd AEs from sediment. The rate constant of metal uptake from the dissolved phase (k _u was greatest for Cd, followed by Zn and Cr in freshwater media. However, in saline water, thek _u of Zn were greater than those of Cd. The influx rate of all tested metals increased with temperature. The efflux rate constant was greatest for Cr (0.02 d^-1), followed by Zn (0.010~0.017 d^-1) and Cd (0.006 d^-1). The efflux rate constant for Zn in clam tissues depurated in 0 psu (0.017 d^-1) was faster than that in 8 psu (0.010 d^-1). Overall results showed that the variation of salinity and temperature in estuarine systems can considerably influence the metal bioaccumulation potential in the estuarine clamC. fluminea. The relatively high Cd accumulation capacity ofC. fluminea characterized by the high AE, high dissolved influx rate and low efflux rate, suggested that this clam species can be used as an efficient biomonitor for the Cd contamination in freshwater and estuarine environments.     

受扰动海域大型底栖动物群落特征及基于AMBI和M-AMBI指数的生态健康评价：以山东烟台辛安河口为例

To understand the ecological status and macrobenthic assemblages of the Xin'an River Estuary and its adjacent waters, a survey was conducted for environmental variables and macrobenthic assemblage structure in September 2012(Yantai, China). Several methods are adopted in the data analysis process: dominance index,diversity indices, cluster analysis, non-metric multi-dimentional scaling ordination, AMBI and M-AMBI. The dissolved inorganic nitrogen and soluble reactive phosphorus of six out of eight sampling stations were in a good condition with low concentration. The average value of DO((2.89±0.60) mg/L) and p H(4.28±0.43) indicated that the research area faced with the risk of ocean acidification and underlying hypoxia. A total of 62 species were identified, of which the dominant species group was polychaetes. The average abundance and biomass was577.50 ind./m2 and 6.01 g/m2, respectively. Compared with historical data, the macrobenthic assemblage structure at waters around the Xin'an River Estuary was in a relatively stable status from 2009 to 2012.Contaminant indicator species Capitella capitata appeared at Sta. Y1, indicating the animals here suffered from hypoxia and acidification. AMBI and M-AMBI results showed that most sampling stations were slightly disturbed,which were coincided with the abiotic measurement on evaluating the health conditions. Macrobenthic communities suffered pressures from ocean acidification and hypoxia at the research waters, particularly those at Stas Y1, Y2 and Y5, which displays negative results in benthic health evaluation.     

Gorgan Bay:a microcosm for study on macrobenthos species-environment relationships in the southeastern Caspian Sea

The relationship between spatial patterns of macrobenthos community characteristics and environmental conditions(salinity, temperature, dissolved oxygen, organic matter content, sand, silt and clay) was investigated throughout the Gorgan Bay in June 2010. Principal components analysis(PCA) based on environmental data separated eastern and western stations. The maximum(4500 ind./m²) and minimum(411 ind./m²) densities were observed at Stas 1 and 6, respectively. Polychaeta was the major group and Streblospio gynobranchiata was dominant species in the bay. According to Distance Based Linear Models results, macrofaunal total density was correlated with silt percentage and salinity and these two factors explaining 64% of the variability while macrofaunal community structure just correlated with salinity(22% total variation). In general, western part of the bay showed the highest number of species and biodiversity while, the highest density was found at Sta. 1 and in the middle part of the bay. Furthermore, relationship between diversity indices and macrobenthic species with measured factors is also discussed. Our results confirm the effect of salinity as an important factor on distribution of macrobenthic fauna in south Caspian brackish waters.     

Distinctive copepod community of the estuarine turbidity maximum: comparative observations in three macrotidal estuaries (Chikugo, Midori, and Kuma Rivers), southwestern Japan

Copepods are considered to be a vital component connecting the unique macrotidal environment to the high productivity and high biodiversity of the Ariake Sea. To examine the spatiotemporal succession of copepod communities, we conducted monthly sampling (vertical hauls of a 100-μm mesh plankton net) in three neighboring macrotidal estuaries between 2005 and 2006. Irrespective of the season, three copepod communities were recognized in relation to the relatively long gradients of salinity and turbidity along the Chikugo and Midori River estuaries. The oligohaline community (salinity 1–10) was observed at higher turbidities (>100 NTU), whereas the freshwater (salinity <1) and meso/polyhaline (salinity >10) communities were associated with lower turbidities (<100 NTU). The oligohaline calanoid Sinocalanus sinensis occurred only in the Chikugo River estuary, maintaining a large biomass (dry weight >10 mg m^?3) in or close to the well-developed estuarine turbidity maximum (ETM) throughout the year. In the Midori River estuary, the oligohaline community lacked S. sinensis and showed a minimum biomass during winter (<10 mg m^?3). In both estuaries, the freshwater community always remained at a small biomass (<1 mg m^?3), whereas the meso/polyhaline community showed marked seasonal changes in biomass (0.1–657 mg m^?3). The prevalence of higher salinities allowed only the meso/polyhaline community to occur in the Kuma River estuary. In summary, S. sinensis characterized the copepod community distinctive of the well-developed ETM, potentially serving as an important link to higher trophic levels during winter when copepods are scarce in other areas.     

Salinity-related variation in gene expression in wild populations of the black-chinned tilapia from various West African coastal marine,estuarine and freshwater habitats

This study measured the relative expression of the genes coding for Na⁺, K⁺-ATPase 1α(NAKA), voltage-dependent anion channel (VDAC), cytochrome c oxidase-1 (COX), and NADH dehydrogenase (NDH), in gills of six wild populations of a West African tilapia species, acclimatised to a range of seasonal (rainy or dry) salinities in coastal, estuarine and freshwater sites. Previous laboratory experiments have demonstrated that these genes, involved in active ion transport, oxidative phosphorylation, and intra-cellular ATP transport, are relatively over-expressed in gill tissues of this species acclimated to high salinity. Positive correlations between relative expression and ambient salinity were found for all genes in the wild populations (Spearman rank correlation, p < 0.05), although for some genes these were only significant in either the rainy season or dry season. Most significantly, however, relative expression was positively correlated amongst the four genes, indicating that they are functionally interrelated in adaptation of Sarotherodon melanotheron to salinity variations in its natural environment. In the rainy season, when salinity was unstable and ranged between zero and 37 psu across the sites, overall mean expression of the genes was higher than in the dry season, which may have reflected more variable particularly sudden fluctuations in salinity and poorer overall water quality. In the dry season, when the salinity is more stable but ranged between zero and 100 psu across the sites, NAKA, NDH and VDAC expression revealed U-shaped relationships with lowest relative expression at salinities approaching seawater, between 25 and 45 psu. Although it is not simple to establish direct relationship between gene expression levels and energy requirement for osmoregulation, these results may indicate that costs of adaptation to salinity are lowest in seawater, the natural environment of this species. While S. melanotheron can colonise environments with extremely high salinities, up to 100 psu, this was related to high relative expression for all genes studied, indicating that this imposes increased energy demand for osmotic homeostasis in gill tissues. This study is the first to demonstrate, in fish and in wild populations, that expression of NAKA, VDAC, NDH and COX are interrelated in gill tissues, and are involved in long-term acclimatisation to a salinity range between 0 and 100 psu.     

Macrobenthic communities of the Vellar Estuary in the Bay of Bengal in Tamil-Nadu in South India

The macrobenthic fauna and communities of the Vellar Estuary located at the southeast cost of India (11°30′ N, 79°45′ E) and the adjacent marine and river habitats are described on the basis of original data (70 samples over 10 transects). The fauna consists of 115 macrobenthic species and 79 species in estuarine habitats. We described 14 types of macrobenthic communities with different compositions of the dominant species. The leading ecological factors of the distribution of the communities are the salinity, depth, and bottom type. The Vellar estuary consists of two longitudinal zones of macrobenthos. The polyhalinic area is populated by the marine species, but it is related not to a salinity decrease but to the protection from waves and silt on the bottom in this area. The polyhalinic communities are most abundant in terms of the biomass and species richness. The mesohalinic area is inhabited by brackish water species and communities with low abundance. The sublittoral estuarine area is dominated by filter-feeders—the bivalves Crassostrea madrasensis, Meretrix casta, Modiolus metcalfei, and Scapharca inaequivalves—and the littoral zone is dominated by the gastropods Cerithidea cingulata, some crabs, and polychaetes. The ecosystem function of the Vellar estuary can be defined as a filter for the fine organic particles transported by the river.     

Distribution patterns of macrobenthic fauna communities in Deukryang Bay,one of the environment conservation areas of Korea

Macrobenthic fauna were collected seasonally at 44 sites in Deukryang Bay from February to November, 2012. The species number of macrobenthic fauna was in the range of 140 to 181, and polychaetes comprised 41.4% of them. The average density of the whole study area changed seasonally from 755 to 1,507 ind. m^?2, and the most abundant fauna group was crustaceans which accounted for 55.1% of total abundance. An amphipod species Nippopisella nagatai was the most dominant species and a decapod species Xenophthalmus pinnotheroides, an amphipod species Photis longicaudata, and a polychaete species Paralacydonia paradoxa were also dominant in all seasons. The mean seasonal values of Shannon’s diversity index (H′) were in the range of 2.2–2.4, and those values for the evenness index and richness index were 0.7–0.7 and 4.6–5.7, respectively. From the cluster analysis, Deukryang Bay could be divided into 3 or 4 station groups with its specific fauna composition. The cluster analysis and an nMDS ordination revealed that local environmental factors such as water depth were related to the spatial delineation of macrobenthic fauna communities in Deukryang Bay.     

Distribution and feeding modes of macrobenthos within three oceanographic feature areas of the KwaZulu-Natal Bight,South Africa

The composition and distribution of macrobenthic communities was investigated in three areas in the KwaZulu- Natal Bight, a section of shelf off the east coast of South Africa. Areas were pre-selected on the basis of three known oceanographic features, posited to deliver land- or Agulhas Current-derived nutrients onto the shelf and to drive ecosystem functioning in this region. Replicate sediment samples were collected with a 0.2 m² van Veen grab, during two surveys (A, B) corresponding with normal periods of high and low rainfall, respectively. A subset of the full station array was selected across the shelf in an arrangement of increasing depths (inner-, mid- and outer shelf) through each feature area to investigate the spatial distribution and feeding modes of macrobenthic taxa. The two periods showed some differences in abundance and numbers of macrobenthic taxa, but were not statistically different. Total macrobenthic abundance from Survey A was 20 215 individuals from 642 taxa, decreasing to 18 000 individuals from 503 taxa during Survey B. Polychaeta and Crustacea were the dominant taxa sampled; abundance of the latter was attributed largely to a proliferation of Paguristes sp.1 at inner-shelf samples in the midbight (Thukela) region during Survey B. Similarity classification distinguished seven sample groups reflecting differences in feature areas and shelf positions under investigation. The Thukela River midshelf community supported the highest macrobenthic abundance, while the midshelf off the southern bight (Durban region) was most species rich. Findings were attributed to the habitat complexity of the midshelf which includes a palaeo-dune cordon at the 60 m isobath. Functionally, the community was dominated by interface- and deposit-feeding fauna, emphasising the importance of trophic plasticity in an environmentally variable and heterogeneous shelf environment.     

Low biomass of macrobenthic fauna at a tropical mudflat: An effect of latitude?

The macrobenthic animal biomass of the intertidal area of the Sembilang peninsula of South Sumatra, Indonesia, has been studied in 2004. Each month (March–August) 21 core samples were taken at each of six sampling stations. Macrobenthic fauna were identified at the lowest taxonomical level possible and counted. Biomass was measured as ash-free dry mass (afdm). The average biomass over all stations and months was 3.62 g afdm m⁻², the highest biomass (47.45 g afdm m⁻²) found at a station in one month was due to abundant occurrence of the bivalve Anadara granosa. Low biomass of macrobenthic fauna at Sembilang peninsula cannot easily be explained but is in line with low biomasses found elsewhere in the tropics. For that reason we analyzed a data set of 268 soft-bottom intertidal biomasses collected world-wide to look for a relationship with latitude. It was shown that average biomass of intertidal macrobenthic fauna in the tropics was significantly (p < 0.05) lower than that at non-tropical sites. A significant second-order relationship between biomass of macrobenthic fauna and latitude was established.     

黄河口海域2004-2009年春季大型底栖动物群落的时空变化

根据 2004年-2009年春季6个航次共186个站次的黄河口附近海域生态调查资料,对该海域的大型底栖动物进行了群落特征分析。调查共采集到大型底栖动物153种,生物量变化范围为6.31~13.20 g/m2,丰度的变化范围为44~902 ind./m2。优势种类历年变化较大,出现频率较高的优势种类为纵沟纽虫、细长涟虫、寡节甘吻沙蚕和绒毛细足蟹;调查区域内丰富度指数及Shannon-Wiener多样性指数历年来呈下降的趋势。聚类结果显示,调查区域大致可分为近岸和远岸2个底栖动物群落。分析表明,水深、底质的中值粒径和海水盐度是影响底栖生物群落结构变化的主要因素。     

环境因素对杭州湾中型浮游动物群落结构的控制作用

A quarterly study of mesozooplankton community structure and environmental variables in the Hangzhou Bay was conducted to examine the response of mesozooplankton community to the variation of water mass and environmental condition. The southeast coast of China is a typical region under the intensive influence of Asia monsoon and freshwater discharge from rivers. The water mass and environmental condition of the Hangzhou Bay, which were influenced by the interaction of currents, freshwater discharge of the Qiantang River and Changjiang River Plume, showed significant seasonal variation. Our results showed that both biomass and abundance were significantly higher in summer((247.7±148.8) mg/m~3 and(350.9±215.6) ind./m~3, respectively)than those in other seasons. Four eco-geographical regions were divided based on the cluster analysis of zooplankton community of the Hangzhou Bay throughout the year, except for winter. Monsoon and the dissolved inorganic nitrogen(DIN) input from freshwater discharge of the Qiantang River and Changjiang River resulted in temporal and spatial variations of environmental gradient in the Hangzhou Bay, which significantly influenced the structure of mesozooplankton community. Redundancy analysis(RDA) indicated that the mesozooplankton community structure was strictly correlated with the DIN gradient, while salinity gradient showed a weak influence in the Hangzhou Bay.     

Modelling salinity and circulation for the Columbia River Estuary

Simulations of the time and depth-dependent salinity and current fields of the Columbia River Estuary have been performed using a multi-channel, laterally averaged estuary model. The study simulated two periods. The first, in October 1980, with low riverflow of about 4,000m³s⁻¹, which showed marked changes in the salinity intrusion processes between neap and spring tides; and second, in spring 1981, with high riverflow varying between 7,000 and 15,000m³s⁻¹, which showed the rapid response of the salinity intrusion to changes in riverflow and that vertical mixing did not change character with increasing tidal energy because of the maintenance of stratification by freshwater flow. An extreme low flow simulation (riverflow of 2,000m³s⁻¹) showed a more partially mixed character of the estuary channels with tidal dispersion of salt across the Taylor Sands from the North Channel to the upper reaches of the Navigation Channel. Asymmetries in the non-linear tidal mean flows, in the flood and ebb circulations, and salinity intrusion characteristics between the two major channels were observed at all riverflows. The model confirms Jay and Smith's (1990) analysis of the circulation processes in that tidal advection of salt by the vertically sheared tidal currents is the dominant mechanism by which the salinity intrusion is maintained against large freshwater flows. An accurate finite-difference method, which minimized numerical dispersion, was used for the advection terms and was an important component in reasonably simulating the October neap-spring differences in the salinity intrusion. The simulations compare favorably with elevation, current and salinity time series observations taken during October 1980 and spring 1981.     

2010-2011年长江河口及邻近水域春夏季仔稚鱼群落结构及其多样性的研究

根据2010—2011年春夏季对长江河口及邻近水域进行了仔稚鱼生态调查,应用单元和多元统计方法分析了春夏季长江河口及邻近水域仔稚鱼群落结构。4个航次调查共获得27个种类的仔稚鱼,隶属5目14科。优势种类主要包括鳀Engraulis japonicus、凤鲚Coilia mystus、康氏小公鱼Stolephorus commersonii、鮻Liza haematocheila、黄姑鱼Nibea albiflora、黄鳍刺虎鱼Acanthogobius flavimanus和寡鳞飘鱼Pseudolaubuca engraulis等。Shannon-Weaver指数(H′)在调查周期内的波动幅度较大,且2011年明显低于2010年。仔稚鱼群落结构和多样性指数春季年间较夏季年间差异性显著。调查区夏季群落结构年间相似性不高,春季群落结构格局年际变化则较明显。聚类分析表明,春夏季长江河口近岸水域仔稚鱼群落可划分为2个站位组,分别对应于长江河口淡水水域和长江口咸水水域。淡水水域组群落和咸水水域组群落总丰度与盐度相关性较高。表明盐度可能是造成长江河口仔稚鱼群落结构时空差异性的主要原因。     

Prediction of salinity intrusion in the sheltered estuary of Terengganu River in Malaysia using 1-D empirical intrusion model

Generally one dimensional(1-D) empirical salinity intrusion model is limited to natural alluvial estuary. However,this study attempts to investigate its ability to model a sheltered alluvial estuary of the Terengganu River in Malaysia. The constructed breakwater at the mouth of the river shelters the estuary from direct influence of the open sea. The salinity density along the estuary was collected during the wet and dry seasons for scenarios before and after the constructed breakwater. Moreover, the freshwater discharges, tidal elevations and bathymetry data were also measured as model inputs. A good fit was demonstrated between simulated and observed variables,namely salinity distribution and intrusion length for both scenarios. Thus, the results show that 1-D empirical salinity model can be utilized for sheltered estuarine condition at the Terengganu Estuary, but with an appropriate determination of an initial point. Furthermore, it was observed that the salinity intrusion in the study area is largely dependent on the freshwater discharge rather than tidal elevation fluctuations. The scale of the salinity intrusion length in the study area is proportional to the river discharge of the –1/2 power. It was appeared that the two lines of the 1-D empirical salinity model and discharge power based equation fitted well to each other, with the average predicted minimum freshwater discharge of 150 m3/s is going to be required to maintain acceptable salinity levels during high water slack(HWS) near the water intake station, which is located at 10.63 km from river mouth.     

珠江口海域a_g(440)遥感模式研究及应用

有色可溶性有机物质(Coloured Dissolved Organic Matter,CDOM)直接影响着海水的光学性质,为水体有机污染物含量遥感反演的基础参数之一。在水色遥感研究领域,一般用440nm波长位置的吸收系数ag(440)来表示其浓度,因而建立ag(440)遥感反演模式,对于掌握相关海域CDOM浓度的空间变化规律及进一步提取其他水环境参数具有重要的作用。利用2013年11月和2014年2月两个航次在珠江口海域现场采集的表观光学量及固有光学量数据,建立了基于HJ-1/CCD卫星传感器的ag(440)遥感反演模型,并应用于珠江口海域,得到该区域2012年1月至2014年6月晴天CDOM浓度空间动态分布图。研究结果表明:(1)现场测定的珠江口海域ag(440)在0.1~0.3m-1,且不同断面ag(440)呈现出一定的规律性变化;(2)利用现场实测数据对遥感模式估算值进行验证,计算出估算值的相对误差为9%,表明所建立模式具有较高的准确率;(3)遥感反演的CDOM空间分布数据与实测数据得到的分布特征基本吻合,整个珠江口及其邻近海域ag(440)的数值范围为0.07~0.31m-1,而且珠江口西部海域ag(440)高于中部和东部海域。     

华南沿海海草床分布区大型底栖动物群落特征初探

为探究华南沿海海草床大型底栖动物群落特征、地区差异及其与海草群落间的关系,2020年在华南沿海12个海草床区域开展了大型底栖动物调查。共布设33个调查断面99个站位,在主要群落参数的基础上,运用相关性分析和聚类分析、nMDS排序、相似性百分比分析等群落生态学统计方法分析了底栖动物群落特征及其与海草群落的关系。共鉴定出大型底栖动物9大门类199种,其中,软体动物种类最多,占总种类数的39.7%。各区域底栖动物的平均栖息密度为155.7 ind/m²,青葛—龙湾(琼海)的平均栖息密度最低,珍珠湾(防城港)的平均栖息密度最高;平均生物量为118.36 g/m²,最低值出现在义丰溪(汕头),最高值出现在珍珠湾。各区域底栖动物的优势种以潮间带泥沙滩常见腹足类、双壳类和多毛类为主;底栖动物的种类多样性指数(H′)平均值为1.12,最低值出现在唐家湾(珠海),最高值出现在铁山港(北海);各调查区域底栖动物主要群落参数大致呈现“北部湾>海南沿岸>珠江口及粤东”的规律。华南沿海海草床分布区大型底栖动物群落的区域性特征较为明显,地理位置相近的海草床底...     

粤西海陵湾养殖区邻近海域大型底栖动物生态学特征

根据2014—2016年粤西海陵湾养殖区湾内和湾外邻近海域21°27′—21°38′N、111°42′—111°57′E 4个航次调查资料,对其大型底栖动物生态学特征进行了研究。结果表明,共鉴定大型底栖动物64种,春季种类最多为39种,秋季最低为17种。4季均以环节动物种类数最多,软体动物次之。不同季节间优势种有所差异,仅倍棘蛇尾Amphioplus sp.为周年优势种。春、夏、秋和冬季第一优势种分别为倍棘蛇尾、菲律宾蛤仔Ruditapes philippinarum、短吻铲荚螠Listriolobus brevirostris和平蛤蜊Mactra mera。平均丰度和生物量分别为213ind./m~2和15.4g/m~2,其中丰度以春季最高为248ind./m~2,夏季最低为167ind./m~2,而生物量则以秋季最高为28.0g/m~2,春季最低为2.4g/m~2;平面分布总体呈现湾外高于湾内的趋势。底栖动物Pielou均匀度和Shannon-Wiener多样性指数分别为0.95—1.00和1.56—4.07,其中时间分布规律明显,春季最高,秋季最低;空间上,两者无明显分布差异。群落结构时空差异显著,为沉积物类型、水深、底层无机氮和悬浮物以及捕食压力等因素共同影响的结果。     

Hydrology of Okarito Lagoon and the inferred effects of selective logging in Okarito Forest

Okarito Lagoon (43° 11′S, 170° 14′E) is a small (20 km²) shore‐parallel, predominantly subtidal estuary, deepest near the landward end, and linked to the sea by two subtidal channels incised through shallow subtidal and intertidal flats which occupy the southern third of the lagoon. Tides at sea vary from 2.1m (spring) to 1.2 m (neap), but in the lagoon the tidal range is constant through the lunar cycle and varies from 0.80 m at the entrance to 0.17 m in the upper lagoon. Tidal water level and flow asymmetries in the subtidal channels are separated by a 1.7 h phase difference. Variations in the net discharge through the inlet result from changing flow cross‐sections rather than from variations in current velocities. Both the tidal‐averaged volume and the tidal compartment of the lagoon vary through the lunar cycle, from maxima at spring tides to minima at neap tides.

Freshwater inflows vary from less than 11 m³.s^‐1 to more than 750 m³.s^‐1. During storms, water level in the lagoon rises rapidly by 2–3 m, then declines to normal over several days. Three water masses, two with salinity and turbidity largely controlled by antecedent rainfall, normally occur in the lagoon. Suspended sediment concentrations in both freshwater inflows and lagoon waters are normally low but increase during floods. Most sediment is supplied by the Waitangi‐taona River or by erosion of tidal channel margins. The lagoon is floored with organic‐rich mud and sandy mud, deposited predominantly from suspension. Surface sediment is consistently muddier than subsurface sediment, probably reflecting an increase in the mud supply since diversion of the Waitangi‐taona River in 1967.

Comparisons of the estimated sediment yield and water inflow effects of the 1967 river diversion with short‐term observations during selective logging suggest that the effects of logging on sediment yield, water balance of the lagoon, and dissolved solids inputs will be small compared with changes caused by diversion of the Waitangi‐taona River.