Assessing the risk of light reduction from natural sediment resuspension events and dredging activities in an inshore turbid reef environment

Bottom trawling represents nowadays one of the most severe anthropogenic disturbances at sea, and determines large impacts on benthic communities and processes. Bottom trawling determines also local sediment resuspension and the effects of the injection of large amounts of surface sediments into the water column have been repeatedly investigated. Few studies have assessed the consequences of sediment resuspension caused by bottom trawling on the quantity, biochemical composition and bioavailability of suspended organic particles and how these eventually rival those exerted by natural storms. To provide insights on this poorly addressed issue, we investigated concentrations and biochemical composition of total and enzymatically digestible pools of particulate organic matter (POM) in the Thermaikos Gulf (Mediterranean Sea) under calm sea conditions, during intensive trawling activities, and after a severe storm. We show here that sediment resuspension caused by trawling can cause large effects on POM quantity, biochemical composition and bioavailability. Both during trawling and after the storm, the relative importance of the carbohydrate pools increased (in the upper water column) and the total lipid concentrations decreased (in the intermediate and bottom layers) when compared to values measured during calm conditions. These results would suggest that bottom trawling could inject in the upper water column POM pools more refractory in nature (<em>e.g</em>., carbohydrates) than those present in calm or after-storm conditions. By contrast, we show also that the bioavailable fraction of biopolymeric C increased significantly during trawling in the upper water column of the shallowest stations and in the bottom water column layer of the deepest ones. These results provide evidence that bottom trawling can influence the overall trophic status of coastal waters, exerting effects similar or stronger than those caused by natural storms, though of variable amplitude depending on the water depth. Since bottom trawling is carried out worldwide and natural storms at sea can be frequent and intense, we claim for the need of assessing new adapting management strategies of bottom trawling in order to mitigate the synergistic impacts of anthropogenic and natural sediment resuspension on coastal biogeochemical cycles.

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Field Observation and Simulation of Sediment Resuspension in a Shallow Lake

Water Science & Technology ◽

10.2166/wst.1988.0211 ◽

1988 ◽

Vol 20 (6-7) ◽

pp. 263-270 ◽

Cited By ~ 4

Author(s):

K. Otsubo ◽

K. Muraoka

Keyword(s):

Numerical Simulation ◽

Shallow Lake ◽

Water Wave ◽

Field Data ◽

Sediment Resuspension ◽

Field Research ◽

Lake Kasumigaura ◽

Bed Erosion ◽

Current Water ◽

Good Agreement

The dispersion and resuspension of sediments in Takahamairi Bay basin of Lake Kasumigaura were studied by means of field research and numerical simulation. The field data on wind direction and velocity, lake current, water wave, and turbidity were shown. Based on these results, we discuss how precipitated sediments were resuspended in this shallow lake. To predict the turbidity and the depth of bed erosion, a simulation model was established for this lake. The calculated turbidity showed good agreement with the field data. According to the simulated results, the turbidity reaches 200 ppm, and the bed is eroded several millimeters deep when the wind velocity exceeds 12 m/s in the lake.

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Submerged Macrophyte Control Using Plastic Blankets

Water Science & Technology ◽

10.2166/wst.1994.0172 ◽

1994 ◽

Vol 29 (4) ◽

pp. 119-126

Author(s):

D. R. Carter ◽

S. Carter ◽

J. L. Allen

Keyword(s):

Plant Species ◽

Sediment Accumulation ◽

Submerged Macrophyte ◽

Light Reduction ◽

Control Options ◽

Macrophyte Growth ◽

Gravel Pits ◽

End Use ◽

Potential Area

Penrith Lakes Scheme is concerned with the rehabilitation of gravel pits to create a system of large recreational lakes. A potential submerged macrophyte problem has been identified in an existing man-made lake. The need to control the macrophytes is dependent on the proposed end use of the lakes and the potential area of invasion. A variety of control options were assessed. Plastic blankets were tested to determine their effectiveness in controlling macrophyte growth specifically in swimming and boat access areas. Comparisons of clear, black and black woven blankets were conducted. Experiments revealed that 90% of the plants under the black and black woven blankets died within six weeks. Under clear blankets plants were reduced by between 20%-90%. Analysis showed that significant interactions occurred between sites and treatments and times, from which it can be inferred that none are independent of each other. Success in the reduction of macrophytes appears dependent on such factors as plant species, sediment accumulation and light reduction.

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Effects of natural sediment features on survival of the phoxocephalid amphipod, Rhepoxynius abronius

Marine Environmental Research ◽

10.1016/0141-1136(88)90006-2 ◽

1988 ◽

Vol 25 (2) ◽

pp. 99-124 ◽

Cited By ~ 75

Author(s):

Theodore H. DeWitt ◽

George R. Ditsworth ◽

Richard C. Swartz

Keyword(s):

Natural Sediment

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Nearshore sediment resuspension and bed morphology.

Journal of Coastal Research ◽

10.2112/si65-269.1 ◽

2013 ◽

Vol 165 ◽

pp. 1593-1598 ◽

Cited By ~ 5

Author(s):

Charlie E. L. Thompson ◽

Hachem Kassem ◽

Jon Williams

Keyword(s):

Sediment Resuspension ◽

Bed Morphology

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Spatial and Temporal Distribution of Cattle Dung and Nutrient Cycling in Integrated Crop–Livestock Systems

Agronomy ◽

10.3390/agronomy10050672 ◽

2020 ◽

Vol 10 (5) ◽

pp. 672

Author(s):

Sandoval Carpinelli ◽

Adriel Ferreira da Fonseca ◽

Pedro Henrique Weirich Neto ◽

Santos Henrique Brant Dias ◽

Laíse da Silveira Pontes

Keyword(s):

Nutrient Cycling ◽

Temporal Distribution ◽

Nutrient Release ◽

Cattle Dung ◽

Total N ◽

Light Reduction ◽

Residue Decomposition ◽

Thiessen Polygon ◽

The Impact ◽

Livestock Systems

Residue decomposition from cattle dung is crucial in the nutrient cycling process in Integrated Crop–Livestock Systems (ICLS). It also involves the impact of the presence of trees exerted on excreta distribution, as well as nutrient cycling. The objectives of this research included (i) mapping the distribution of cattle dung in two ICLS, i.e., with and without trees, CLT and CL, respectively, and (ii) quantification of dry matter decomposition and nutrient release (nitrogen—N, phosphorus—P, potassium—K, and sulphur—S) from cattle dung in both systems. The cattle dung excluded boxes were set out from July 2018 to October 2018 (pasture phase), and retrieved after 1, 7, 14, 21, 28, 56 and 84 days (during the grazing period). The initial concentrations of N (~19 g kg−1), P (~9 g kg−1), K (~16 g kg−1), and S (~8 g kg−1) in the cattle dung showed no differences. The total N, P, K and S released from the cattle dung residues were less in the CLT system (2.2 kg ha−1 of N; 0.7 kg ha−1 of P; 2.2 kg ha−1 of K and 0.6 kg ha−1 of S), compared to the CL (4.2 kg ha−1 of N; 1.4 kg ha−1 of P; 3.6 kg ha−1 of K and 1.1 kg ha−1 of S). Lesser quantities of cattle dung were observed in the CLT (1810) compared to the CL (2652), caused by the lower stocking rate, on average, in this system (721 in the CL vs. 393 kg ha−1 in the CLT) because of the reduced amount of pasture in the CLT systems (−41%), probably due to light reduction (−42%). The density of the excreta was determined using the Thiessen polygon area. The CL system revealed a higher concentration of faeces at locations near the water points, gate and fences. The CLT affects the spatial distribution of the dung, causing uniformity. Therefore, these results strengthen the need to understand the nutrient release patterns from cattle dung to progress fertilisation management.

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