Biogeochemical aspects of bottom anoxia in a Mediterranean lagoon (Thau, France)
Biogeochemical aspects of bottom anoxia in a Mediterranean lagoon (Thau, France)
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DOI：
10.3354/meps164135
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发表时间：
1998-01-01
影响因子：
2.5
通讯作者：
Deslous-Paoli, JM
中科院分区：
文献类型：
--
作者：
Souchu, P;Gasc, A;Deslous-Paoli, JM
理化特性在位于Thau泻湖最深处的一个站点测量了（温度、盐度、溶解氧）、营养物[溶解无机氮（DIN）、可溶活性磷（SRP）和硅酸盐]、溶解有机氮（DON）和磷以及颗粒物[颗粒有机碳（POC）和氮（PON）和叶绿素a（8.5米），法国，在10天的底部缺氧期间，在1994年夏天。上部8厘米的沉积物进行了分析，铵（NH 4+）和SRP浓度的孔隙水。研究期间的特点是平均风速低于4 m s（-1），导致表面温度从18 ° C增加到29 ° C，形成温跃层。前一天平均风速与底层和表层温度差之间的相关性（p < 10（-4））表明，风是垂直混合的主要矢量。风的缺乏导致溶解氧耗尽底部2米，并在沉积物的上部10厘米（80至>95%）的孔隙度增加。缺氧条件下，孔隙水中的NH 4+和SRP浓度分别从231 +/- 89增加到1305 +/- 305（+/- SD）μ M和从6.6 +/- 0.8增加到108 +/- 43 μ M。从矿化的microphytobenthos的孔隙水中的NH 4+浓度的潜在增加解释了30%的测量增加的上部8厘米的孔隙水。研究期间的特点是增加NH 4 + SRP和溶解硅浓度在底部水柱（最大分别为24.2，4.9和57 μ M）。营养盐浓度在水柱和温度之间的线性回归揭示了一个强大的增强缺氧期间的底部通量。硝酸盐+亚硝酸盐（NO3- + NO2-）在缺氧沃茨中不存在，在好氧沃茨中保持在0.5 μ M以下。从1970年到1994年，陶泻湖的水柱中SRP的月浓度显示缺氧事件，夏季峰值对应于强底部缺氧。但总的趋势是减少，这是由于富营养化的逐步控制，这将导致在未来十年内消失的底部缺氧。一部分底栖来源的营养物质通过初级生产转化为浮游颗粒物质，使chia的浓度从约1 μ g l（-1）增加到15 μ g l（-1）。DON和PON在水柱中的浓度显着相关，这表明DON化合物被释放的浮游食物网，但不直接由沉积物。在风速小于5 m s（-1）的10 d内，将水柱视为封闭箱，总氮（DIN + DON + PON）的增加估计为1.7 μ mol N l（-1）d（-1），相当于10 d内600 μ mol N m（-1）h（-1）的底栖通量。
Physical and chemical characteristics (temperature, salinity, dissolved oxygen), nutrients [dissolved inorganic nitrogen (DIN), soluble reactive phosphorus (SRP) and silicate], dissolved organic nitrogen (DON) and phosphorus and particulate matter [particulate organic carbon (POC) and nitrogen (PON) and chlorophyll a] were measured at a station located in the deepest part of the Thau lagoon (8.5 m), France, during a 10 d period of bottom anoxia in summer 1994. The upper 8 cm of sediment were also analyzed for ammonium (NH4+) and SRP concentrations in the porewater. The study period was characterized by mean wind speed under 4 m s(-1) which induced an increase of surface temperature from 18 to 29 degrees C with the formation of a thermocline. The correlation (p < 10(-4)) between the wind speed averaged over the previous day and the difference between bottom and surface temperatures showed that the wind constituted the main vector of vertical mixing. The lack of wind led to dissolved oxygen depletion in the bottom 2 m and to a strong porosity increase in the upper 10 cm of sediment (80 to >95%). Anoxic conditions increased NH4+ and SRP concentrations in porewater from 231 +/- 89 to 1305 +/- 305 (+/- SD) mu M and from 6.6 +/- 0.8 to 108 +/- 43 mu M respectively. The potential increase of NH4+ concentrations in porewater estimated from the mineralization of the microphytobenthos explained 30% of the measured increase in the upper 8 cm of porewater. The study period was characterized by an increase in NH4+ SRP and dissolved Si concentrations in the bottom water column (maxima respectively 24.2, 4.9 and 57 mu M). Linear regressions between nutrient concentrations in the water column and temperature revealed a strong enhancement of bottom fluxes during anoxia. Nitrate + nitrite (NO3- + NO2-) were absent in anoxic waters and remained below 0.5 mu M in oxic waters. Monthly concentrations of SRP in the water column of the Thau lagoon from 1970 to 1994 revealed anoxia events by summer peak values corresponding to strong bottom anoxia. Nevertheless, the general trend was a decrease due to the gradual control of eutrophication which should lead to the disappearance of bottom anoxia within the next decade. A fraction of the nutrients of benthic origin was transformed into planktonic particulate matter via primary production which increased the concentrations of chi a from about 1 to 15 mu g l(-1). Concentrations of DON and PON in the water column were significantly correlated, suggesting that DON compounds were released by the pelagic food web but not directly by the sediment. The increase of total nitrogen (DIN + DON + PON), considering the water column as a closed box during 10 d of winds under 5 m s(-1), was estimated at 1.7 mu mol N l(-1) d(-1) and would correspond to a benthic flux of 600 mu mol N m(-1) h(-1) for 10 d.