Will enhanced turbulence in inland waters result in elevated production of autochthonous dissolved organic matter?

Chromophoric dissolved organic matter (CDOM) is crucial in the biogeochemical cycle and carbon cycle of aquatic environments. However, in inland waters, remotely sensed estimates of CDOM remain challenging due to the low optical signal of CDOM and complex optical conditions. Therefore, developing efficient, practical and robust models to estimate CDOM absorption coefficient in inland waters is essential for successful water environment monitoring and management. We examined and improved different machine learning algorithms using extensive CDOM measurements and Landsat 8 images covering different trophic states to develop the robust CDOM estimation model. The algorithms were evaluated via 111 Landsat 8 images and 1708 field measurements covering CDOM light absorption coefficient a(254) from 2.64 to 34.04 m−1. Overall, the four machine learning algorithms achieved more than 70% accuracy for CDOM absorption coefficient estimation. Based on model training, validation and the application on Landsat 8 OLI images, we found that the Gaussian process regression (GPR) had higher stability and estimation accuracy (R2 = 0.74, mean relative error (MRE) = 22.2%) than the other models. The estimation accuracy and MRE were R2 = 0.75 and MRE = 22.5% for backpropagation (BP) neural network, R2 = 0.71 and MRE = 24.4% for random forest regression (RFR) and R2 = 0.71 and MRE = 24.4% for support vector regression (SVR). In contrast, the best three empirical models had estimation accuracies of R2 less than 0.56. The model accuracies applied to Landsat images of Lake Qiandaohu (oligo-mesotrophic state) were better than those of Lake Taihu (eutrophic state) because of the more complex optical conditions in eutrophic lakes. Therefore, machine learning algorithms have great potential for CDOM monitoring in inland waters based on large datasets. Our study demonstrates that machine learning algorithms are available to map CDOM spatial-temporal patterns in inland waters.

Download Full-text

Risk analysis of dissolved organic matter-mediated ultraviolet B exposure in Canadian inland waters

Canadian Journal of Fisheries and Aquatic Sciences ◽

10.1139/f04-165 ◽

2004 ◽

Vol 61 (12) ◽

pp. 2511-2521 ◽

Cited By ~ 28

Author(s):

L A Molot ◽

W Keller ◽

P R Leavitt ◽

R D Robarts ◽

M J Waiser ◽

...

Keyword(s):

Climate Change ◽

At Risk ◽

Organic Matter ◽

Dissolved Organic Matter ◽

Ultraviolet B ◽

Aquatic Systems ◽

Inland Waters ◽

Direct Exposure ◽

Risk Of Exposure ◽

Ozone Levels

With depleted ozone levels and the possibility that climate change might lower dissolved organic matter (DOM) concentrations, the risk of exposure of fresh waters in Canada to ultraviolet B (UV-B) was evaluated. First, the distribution of a UV-B-sensitive zooplankton genus, Daphnia, was examined as a function of DOM concentration and maximum depth (Zmax) in 258 systems. Distribution was not restricted by UV-B, although very clear, shallow systems are underrepresented. Secondly, the depth at which 1% of surface radiance at 320 nm occurs (Z320,1%) was compared with Zmax in over 1000 aquatic systems in 15 ecozones to determine the proportions of optically clear systems (Zmax ≤ Z320,1%) and systems that may become clear (i.e., are "at risk") should DOM decrease by 50%. South of the treeline, <6% of systems were clear, with the exception of two ecozones with 10%20%. The proportion of systems at risk was 0% in most regions, with 5%9% in four regions. DOM levels appear adequate to prevent extirpation of sensitive taxa like Daphnia through direct exposure to UV-B in most regions south of the treeline. However, optically clear and at-risk ponds were much more common in the three Artic ecozones, especially the Northern Arctic and Arctic Cordillera.

Download Full-text

Reactivity, fate and functional roles of dissolved organic matter in anoxic inland waters

Biology Letters ◽

10.1098/rsbl.2019.0694 ◽

2020 ◽

Vol 16 (2) ◽

pp. 20190694 ◽

Cited By ~ 2

Author(s):

Maximilian P. Lau ◽

Paul del Giorgio

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Inland Waters ◽

Aquatic Environments ◽

Anoxic Conditions ◽

Functional Roles ◽

Network Scale ◽

Aquatic Compartment ◽

Global Cycle

The transit of organic matter (OM) through the aquatic compartment of its global cycle has been intensively studied, traditionally with a focus on the processing and degradation of its dissolved fraction (dissolved organic matter, DOM). Because this is so intimately related to oxidation, the notion tenaciously persists that where oxygen is absent, DOM turnover is markedly slowed. In this Opinion Piece, we outline how diverse processes shape, transform and degrade DOM also in anoxic aquatic environments, and we focus here on inland waters as a particular case study. A suite of biogeochemical DOM functions that have received comparatively little attention may only be expressed in anoxic conditions and may result in enhanced biogeochemical roles of these deoxygenated habitats on a network scale.

Download Full-text

Performance of existing QAAs in Secchi disk depth retrieval in phytoplankton and dissolved organic matter dominated inland waters

Journal of Applied Remote Sensing ◽

10.1117/1.jrs.12.036017 ◽

2018 ◽

Vol 12 (03) ◽

pp. 1 ◽

Cited By ~ 1

Author(s):

Thanan Rodrigues ◽

Enner Alcântara ◽

Deepak R. Mishra ◽

Fernanda Watanabe ◽

Nariane Bernardo ◽

...

Keyword(s):

Organic Matter ◽

Dissolved Organic Matter ◽

Inland Waters ◽

Secchi Disk ◽

Secchi Disk Depth

Download Full-text

Enhanced bioavailability of dissolved organic matter (DOM) in human-disturbed streams in Alpine fluvial networks

Biogeosciences ◽

10.5194/bg-19-187-2022 ◽

2022 ◽

Vol 19 (1) ◽

pp. 187-200

Author(s):

Thibault Lambert ◽

Pascal Perolo ◽

Nicolas Escoffier ◽

Marie-Elodie Perga

Keyword(s):

Land Use ◽

Organic Matter ◽

Dissolved Organic Matter ◽

Human Disturbance ◽

Human Activities ◽

Urban Streams ◽

Bacterial Respiration ◽

Inland Waters ◽

C Cycle ◽

The Impact

Abstract. The influence of human activities on the role of inland waters in the global carbon (C) cycle is poorly constrained. In this study, we investigated the impact of human land use on the sources and biodegradation of dissolved organic matter (DOM) and its potential impact on bacterial respiration in 10 independent catchments of the Lake Geneva basin. Sites were selected along a gradient of human disturbance (agriculture and urbanization) and were visited twice during the winter high-flow period. Bacterial respiration and DOM bioavailability were measured in the laboratory through standardized dark bioassays, and the influence of human land uses on DOM sources, composition and reactivity was assessed from fluorescence spectroscopy. Bacterial respiration was higher in agro-urban streams but was related to a short-term bioreactive pool (0–6 d of incubation) of autochthonous origin, whose relative contribution to the total DOM pool increased with the degree of human disturbance. On the other hand, the degradation of a long-term (6–28 d) bioreactive pool related to terrestrial DOM was independent from the catchment land use and did not contribute substantially to aquatic bacterial respiration. From a greenhouse gas emission perspective, our results suggest that human activities may have a limited impact on the net C exchanges between inland waters and the atmosphere, as most CO2 fixed by aquatic producers in agro-urban streams is cycled back to the atmosphere after biomineralization. Although seasonal and longitudinal changes in DOM sources must be considered, the implications of our results likely apply more widely as a greater proportion of autochthonous-DOM signature is a common feature in human-impacted catchments. Yet, on a global scale, the influence of human activities remains to be determined given the large diversity of effects of agriculture and urbanization on freshwater DOM depending on the local environmental context.

Download Full-text