Methane Emissions from Surface of Mangrove River on Hainan Island, China

The surfaces of rivers are considered important sources of atmospheric methane (CH4), however research on this topic is still constrained, especially in freshwater rivers and with the consideration of spatial heterogeneity. Three regions (upper reaches, midstream and downstream) were selected to examine the CH4 fluxes from a freshwater river surface in a mangrove forest wetland from 2012 to 2013, using floating chambers. Results showed that the CH4 fluxes varied significantly among the three regions, with the lowest fluxes at downstream (0.50 ± 0.20 mg m−2 h−1), and highest at upper reaches (1.19 ± 0.36 mg m−2 h−1). The average emission rate at midstream was 0.95 ± 0.37 mg m−2 h−1. The methane flux also varied with seasons, with higher flux in rain-abundant seasons. On average, the CH4 flux in our research river was 0.88 ± 0.31 mg m−2 h−1, which was less than other tropical rivers. In addition, we found that the CH4 flux was significantly correlated with the water characteristics of temperature and atmospheric pressure. Thereby, this study quantified the methane emission from a freshwater river surface in a tropical mangrove forest, enriching the existing knowledge of river surface CH4 flux.

Species of Fish in rivers in the Northern Peninsula of Sulawesi Island

This study aims to determine the species of fish found in the Poigar River, Ranoyapo River, Maruasey River, Talawaan River, and Likupang River in the northern peninsula of Sulawesi Island. These five rivers empty into the Sulawesi Sea. Sampling was carried out in the upstream, middle and downstream parts of the river, all sampling areas were freshwater areas, estuary areas with brackish water types were not included in this study. Sampling was carried out using cast nets and electric shocks. There are 58 species (16 orders, 21 families, 40 genera). Families Gobidae (9 genera, 19 species) and Eleotridae (8 genera 13 species), 19 other families have only 3 or 2 or 1 species. There are 28 species of Ranoyapo River, 25 species of Maruasey River, 23 species of Poigar River, 15 species of Likupang River, and 9 species of Talawaan River. Eel Anguilla marmorata widely distributed in five rivers, and Eleotris melanosoma (Eleotridae) Osteochilus hasseltii (Cyprinidae) in four rivers. The other species are only found in 3, 2, and 1 rivers. There are 27 species found in only one river.Keywords: Freshwater; River; Species; Fish.AbstrakPenelitian ini bertujuan untuk mengetahui spesies ikan yang terdapat di Sungai Poigar, Sungai Ranoyapo, Sungai Maruasey, Sungai Talawaan dan Sungai Likupang di semenanjung utara Pulau Sulawesi. Lima sungai ini bermuara di Laut Sulawesi. Pengambilan sampel dilakukan pada bagian hulu, tengah dan bagian hilir sungai, seluruh wilayah pengambilan sampel adalah wilayah air tawar, daerah muara dengan tipe air payau tidak termasuk dalam penelitian ini. Pengambilan sampel dilakukan dengan menggunakan jaring lempar dan kejutan listrik. Terdapat 58 spesies (16 ordo, 21 famili, 40 genus). Famili Gobidae (9 genus, 19 spesiies) dan Eleotridae (8 genus 13 spesies), 19 Famili yang lain hanya memiliki 3 atau 2 atau 1 spesies. Sungai Ranoyapo terdapat 28 spesies, Sungai Maruasey 25 spesies, Sungai Poigar 23 spesies, Sungai Likupang 15 spesies dan Sungai Talawaan 9 spesies. Ikan sidat Anguilla marmorata menyebar luas pada lima sungai, dan Eleotris melanosoma (Eleotridae) Osteochilus hasseltii (Cyprinidae) pada empat sungai. Spesies yang lain hanya ditemukan pada 3, 2 dan 1 sungai. Terdapat 27 spesies yang ditemukan hanya pada satu sungai.Keywords: Freshwater; River; Species; Fish.

Problems of Shapour River Salinity Rising Over Recent Prolonged Streamflow Reduction Period and Solutions of River Salinity Management: An Originally Freshwater River Intensively Salinized by Natural Salinity Sources

The Shapour river with catchment area of 4254 km2 is a major river system in southern Iran. While the upstream river flow (the upper Shapour river) is fresh, it becomes extremely salinized at the downstream confluence of Shekastian salty tributary and the entering nearby Boushigan brine spring. The river then passes through the Khesht plain and finally discharges into the Raeisali-Delvari storage dam, which went into operation in 2009. Over the 2006–2019 period, reduced precipitation and over-utilization of freshwater resources resulted in ~ 72% streamflow reduction in the Shapour river. Consequently, the ratios of unused salty/brine water of Shekastian tributary and Boushigan spring to fresh-outflow of the upper Shapour river increased by ~ 3 times and river salinity fluctuation domain at the Khesht plain inlet dramatically increased from 2.1-4.0 dS m− 1 to 3.7–26.0 dS m− 1. It also resulted in disappearance of most river aquatic species and caused major economic damages in the middle Shapour river. On the seasonal time-scale, consecutive processes of salt accumulation during irrigation season of the Khesht plain date orchards and then salt drainage during rainy season have adjusted salinity fluctuation domain from 3.7–26.0 dS m− 1 at the plain inlet to 5.2–8.9 dS m− 1 at the plain outlet. In the lower Shapour river, storage/mixing of fresh/salty inflow waters in the Raeisali-Delvari reservoir has adjusted strong salinity fluctuation domain from 0.9–10.7 dS m− 1 at the reservoir inlet to 3.6–5.5 dS m− 1 at the reservoir outlet. Success of the Raeisali-Delvari reservoir for salinity adjustment is due to its suitable location on the Shapour river, by being situated on downstream of all of the main river tributaries with natural saline/fresh sources of water. Therefore, construction of storage dam on proper site in conjunction with controlled freshwater utilization are viewed as effective measures for salinity management of subjected rivers to natural salinity sources.

Salinity effects on pressure-based tide gauges in a macro-tidal estuary

<div>Estuarine salinity can be highly variable, resulting in significant density variability. So tide-gauges measuring pressure (either directly or as bubblers) can experience salinity-induced pressure variations of up to 1% of their range. They can therefore record depths with up to 1% variability that is not seen in other measurement systems. In most places this is a small effect compared to other sources of varibility but in macro-tidal estuary such as the Severn in the UK it amounts around 10cm difference between high and low tide. This is comparable to levels of accuracy being sought by current surge forecasts. </div><div> </div><div>This effect can be seen in neighbouring radar and pressure gauges in the Severn. It could result in spurious seasonal and spring-neap constituents. Elsewhere, similar errors could result related to unusual freshwater river flow in estuarine locations that are usually saline, or unusual saline storm surge in usually freshwater sites. It has implications for assessment of storm surge and multi-hazard forecasting, and accurate calibration of new gauge installations.  </div><div> </div>