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Climate anomalies, urban expansion, and strong disturbances from human activities have maintained high levels of nitrogen-containing nutrients in many productive or functional lakes for a long time, and nitrogen, as a key nutrient element affecting the eutrophication of lakes, is closely related to the structure and composition of dissolved organic matter (DOM) in water bodies.
DOM in aquatic environments includes exogenous DOM from human activities such as domestic sewage, industrial wastewater and agricultural runoff, as well as a large number of endogenous DOMs provided by aquatic plants that degenerate large areas of lakes, and are therefore complex and heterogeneous.
DOM can be used as a carbon source and nutrient affecting the activity of microorganisms, and different sources and their proportions determine their bioavailability, but the interaction relationship between nitrogen, DOM and microorganisms is not clear in the degradation of lakes, and the coupling mechanism is rarely studied
.
Recently, the team of Wu Zhenbin, a researcher at the Institute of Hydrobiology, Chinese Academy of Sciences, took Honghu, a typical large shallow lake in the middle and lower reaches of the Yangtze River (Figure 1), and analyzed the spatial heterogeneity and coupling correspondence between different spatial nitrogen morphological composition, DOM composition, humification degree, and the intrinsic response relationship between microorganisms as the starting points.
The internal causes of nitrogen accumulation at the micro-interface of the lake-flood lake ecosystem in the typical degradation of the middle and lower reaches of the Yangtze River were revealed (Figure 2).
Figure 1: Distribution of sampling sites in Honghu Lake
Figure 2: Patterns of responses of different morphological nitrogen, DOM and microbial communities
The results show that the distribution of different forms of inorganic nitrogen in Honghu Lake shows spatial heterogeneity with the direction of the flow field (Figure 3).
The nitrate content of the overlying water at the mouth of the lake was high, while the ammonia nitrogen content was higher in the artificial breeding enclosure in the northwest region, and the total nitrogen accumulation showed a high accumulation
in the southwest and northeast regions.
The main form of nitrogen in Honghu sediment is organic nitrogen, and the content of ammonia nitrogen is the highest
in inorganic nitrogen sources.
The sediment characteristics with strong polarity and high concentration nutrient adsorption capacity (high proportion of silt components) led to high
levels of total nitrogen and ammonia nitrogen in the southwest region.
In addition, the widespread decline of aquatic plants has exacerbated the accumulation
of nitrogen in sediments in the southwest region.
The low abundance of bacteria associated with nitrogen cycling in sediments affects nitrogen bioavailability and transformation, and ultimately directly leads to increased
nitrogen content in sediments.
Under the influence of local hydrological and biogeochemical processes, the content of sediment organic matter increased from the mouth of the lake to the lake area.
Due to the joint influence of exogenous and endogenous DOM pollution, the distribution and transformation of DOM humus components showed large spatial differences, the inlet topography, the high proportion of fine clay, and a large number of foreign nutrients and organic matter, which made the inlet sediment with the highest degree of humus (Figure 4).
The ecological relationship between nitrogen, DOM and microbial communities further suggests that the coupling of nitrogen, DOM and physicochemical properties in sediments directly or indirectly affects the abundance and diversity of bacterial communities (Figure 5).
In addition, the ecological response of microbes is ultimately fed back into organic matter migration and nutrient accumulation
.
The internal ecological response laws of nitrogen, DOM and microorganisms in the degraded lake environment found in this study clarify the relationship between nutrient enrichment and bioavailability in the ecosystem of degraded lake, which is of great significance for predicting the dynamic change of the feedback cycle mechanism of the degraded system, and will provide scientific support
for the formulation of comprehensive management countermeasures for the restoration of degraded lake water ecology.
Fig.
3 Spatial distribution characteristics of TN, NH4+-N and NO3--N in overlying water (A/B/C/D) and sediment (E/F/G/H) of Honghu Lake
Fig.
4: Changes in the composition of humus in sediments and the projected values of DOM optical parameters (R-estuarine area; S-Southwest region; W-Northwest Region; E-Northeast region; HS-humus; HA-humic acid; FA-Fulvic acid)
Figure 5: Analysis
of structural equations for environmental factors of bacterial community diversity.
Arrows represent direct causal paths, while double-headed arrows represent paired covariates
.
Solid lines with different line widths indicate significant impact (*P< 0.
05, **P< 0.
01, P< 0.
001), and gray lines indicate no significant impact
.
The number next to the arrow indicates the effect size
of the relationship.
R2 represents the proportion of the
variance being explained.
The red and blue lines indicate positive and negative relationships
, respectively.
(BIX\FI\HIX\SUVA 254\A250/A365 are DOM spectral parameters; pH/ORP/Sand/Silt are sedimentary physical and chemical properties; DB-bacterial diversity)
The research was supported by the National Natural Science Foundation of China (31830013; 32171632； 32101374) and Hubei Provincial Key Research and Development Program (2020BCA073) and other projects to support "Spatial characteristics of nitrogen forms in a large.
" degenerating lake: its relationship with dissolved organic matter and microbial community" in the Journal of Cleaner Production Published, (https://doi.
org/10.
1016/j.
jclepro.
2022.
133617).
Dr.
Lu Zhang, Special Research Assistant, is the first author, and Prof.
Biyun Liu is the corresponding author
.
Researcher Wu Zhenbin gave guidance
to the research work.
Recently, the research team has carried out a series of studies on the decline of submerged plants in eutrophication lakes and the abnormal proliferation mechanism of lower algae, and the main results are detailed in the following related links:
Zhang, L.
, Huang, S.
Z.
, Peng, X.
, Liu, B.
Y.
*, Zhang, X.
Y.
, Ge, F.
J.
, Zhou, Q.
H.
, Wu, Z.
B.
, 2021.
Potential ecological implication ofCladophora oligocloradecomposition: Characteristics of nutrient migration, transformation, and response of bacterial community structure.
Water Research.
190, 116741.
（https://doi.
org/10.
1016/j.
watres.
2020.
116741）
Zhang, L.
,Ge, F.
J.
, Zhang, S.
X.
, Li, X.
, Peng, X.
, Zhang, X.
Y.
, Zhou, Q.
H.
, Wu, Z.
B.
, Liu, B.
Y.
*, 2022.
Potential effects ofCladophora oligocloradecomposition: Microhabitat variation andMicrocystis aeruginosagrowth response.
Ecotoxicology and Environmental Safety.
247, 114236.
（https://doi.
org/10.
1016/j.
ecoenv.
2022.
114236）
Peng, X.
, Zhang, L.
, Li, Y.
, Lin, Q.
W.
, He, C.
, Huang, S.
Z.
, Li, H.
, Zhang, X.
Y.
, Liu, B.
Y.
*, Ge, F.
J.
, Zhou, Q.
H.
, Zhang, Y.
, Wu, Z.
B.
, 2021.
The changing characteristics of phytoplankton community and biomass in subtropical shallow lakes: Coupling effects of land use patterns and lake morphology.
Water Research.
200, 117235.
（https://doi.
org/10.
1016/j.
watres.
2021.
117235）
Peng, X.
, Lin, Q.
W.
, Liu, B.
Y.
*, Huang, S.
Z.
, Yan, W.
H.
, Zhang, L.
, Ge, F.
J.
, Zhang, Y.
, Wu, Z.
B.
, 2022.
Effect of submerged plant coverage on phytoplankton community dynamics and photosynthetic activity in situ.
Journal of Environmental Management.
301, 113822.
（https://doi.
org/10.
1016/j.
jenvman.
2021.
113822）
