Functional properties of soils formed from biochemical ripening of dredged sediments—subsidence mitigation in delta areas

Abstract

Purpose In delta areas, dense networks of canals have been developed through time and have to be periodically dredged. Lowering the groundwater level in delta areas deepens the aerobic zone, leading to the oxidation of organic matter and possibly to land subsidence. The use of the dredged sediments on land can be a solution to mitigate land subsidence in delta areas. Materials and methods Five types of dredged sediments with different organic matter content and particle size distribution were dewatered for 7 days and then submitted to biochemical ripening during 141 days on a laboratorial scale with constant temperature and relative humidity. The functional properties analysed were the type and content of organic matter, pH, total C, N, P and S, dry bulk density, water retention capacity, aggregate stability and load-bearing capacity. Results and discussion After biochemical ripening, there was no significant loss in the mass of organic matter but there was an increase in the fraction of stable organic compounds, observed by an increase in oxygen-bearing compounds and a decrease in hydrocarbons during biochemical ripening. The pH was not affected by biochemical ripening, and the total C, N, P and S concentrations are high and therefore the dredged sediments can improve the quality of the land. Most volume lost during dewatering and biochemical ripening can be attributed to the loss of water. The water retention capacity of the dredged sediments changed with biochemical ripening. The soils formed from biochemical ripening have very stable aggregates, and its load-bearing capacity is enough to sustain cattle and tractors. Conclusions Most volume lost during dewatering and biochemical ripening can be attributed to the loss of water and not organic matter. Therefore, the studied dredged sediments have potential to mitigate land subsidence in delta areas when spread on land.

Subsidence of organic dredged sediments in an upland deposit in Wormer- en Jisperveld: North Holland, the Netherlands

“…This is also in line with previous observations on lab scale (Oliveira et al 2017) and meso-scale experiments (Oliveira et al 2018, In Press) using sediments dredged from the same location.…”

“…Previous studies with the same sediments have shown that the water retention capacity of the sediments dredged from the same location varies from 0.71 cm 3 water /cm 3 dry matter before ripening to 1.02 after ripening for a pF = 2 (Oliveira et al 2017), and the high water content can protect the organic matter from mineralization.…”

“…This solution could also protect higher extensions of peatland from aerobic conditions since the sediments have a high water retention capacity. Laboratory scale experiments with samples of 1,5 cm height of the same sediments have shown that after 141 days at 20 °C the organic matter mineralization was negligible, and the samples had enough undrained shear strength to sustain cattle and tractors (Oliveira et al 2017). The solution of thinner layers would not only limit air penetration due to the high water retention capacity but also allow shallower groundwater tables which is a complementary measure to reduce land subsidence Querner et al 2012).…”

“…The type of organic matter was characterized with the Rock-Eval 6 ® method, described in (Oliveira et al 2017). The Rock-Eval ® analysis of columns 3-5 and 7-10 was done in one batch, and the analysis of columns 11-12 was done in a second batch.…”

Assessing the effects of lake‐dredged sediments on soil health: Agricultural and environmental implications for northwestern Ohio

“…The soil physicochemical properties, the soybean aboveground and belowground biomass and yield, and the chemical composition of percolated solutions were investigated using a greenhouse approach. It is well established that high content of soil organic C increases soil fertility, soil stabilization, soil structure, water holding capacity, and crop productivity (Kögel‐Knabner & Rumpel, 2018; Newcomb et al., 2017; Oliveira et al., 2017). Studies have shown that average bulk density decreased with increasing dredged sediment ratios, allowing for better root penetration, increased water infiltration, higher porosity, and greater water holding capacity (Wang et al., 2014).…”