Analyzing the status of submerged aquatic vegetation using novel optical parameters

Abstract

The reservoirs constructed throughout Brazil for electrical power generation following its industrial and socioeconomic development now favour abundant aquatic macrophyte growth. Nova Avanhandava Reservoir is fully inhabited by submerged aquatic vegetation (SAV) that poses serious ecological and economic threats. The overall goal of this study was to assess the radiation availability in the water column in the Nova Avanhandava Reservoir and analyse its influence on SAV development and growth. In addition to the diffuse attenuation coefficient (K d) and euphotic zone depth (Z EZ), optical parameters such as percentage light through the water (PLW) were computed and analysed to achieve the objective. Nineteen sampling locations were considered for both spectroradiometer measurements and water sampling for analytical determination of total suspended solids (TSS) and chlorophyll-a concentration. Depth, SAV height, and precise position were also collected through hydro-acoustic measurements. The upstream region showed the highest TSS and K d levels compared to the downstream. SAV heights were found to be lower upstream compared to downstream. The growth of tall SAV was favoured by low PLW, which grew taller to intercept required radiation. Locations with high transparency (lower K d) also favoured the development of tall SAV compared to areas of high K d. This may mean that low PLW values favour tall SAV growth if K d is low enough not to hinder this. An inverse relationship between SAV height and attenuation of photosynthetic active radiation (K d,PAR) was observed with a coefficient of determination of R 2 = 0.56 (p < 0.001), demonstrating that SAV height can be estimated using K d,PAR with significant accuracy.

Kd(PAR) and a Depth Based Model to Estimate the Height of Submerged Aquatic Vegetation in an Oligotrophic Reservoir: A Case Study at Nova Avanhandava

“…Upstream areas are relatively shallow compared to the downstream areas, which could cause resuspension of bottom sediments induced by strong winds and water flow [1,48]. In downstream areas, the slow water flow due to the proximity of the dam and higher depths favored the deposition of suspended solids on the bottom, which resulted in a lower K d(PAR) , as shown by Rotta et al [15]. The region with a high K d(PAR) was observed near Figure 4a, and is probably caused by the presence of a sand mining company, indicated by the black arrow in Figure 4.…”

“…The region with a high K d(PAR) was observed near Figure 4a, and is probably caused by the presence of a sand mining company, indicated by the black arrow in Figure 4. Sand dredging leads to sediment resuspension that increased the K d values at nearby locations [15]. Based on the K d(PAR) map, it can be stated that most of these particles resuspended from the bottom were deposited again at locations approximately 2 km beyond the extraction point.…”

Analyzing the feasibility of a space-borne sensor (SPOT-6) to estimate the height of submerged aquatic vegetation (SAV) in inland waters

“…Rotta et al (2012) mapped SAV in the Porto Colômbia Reservoir (Uberaba River, Minas Gerais State) using an echosounder detecting presence of SAV up to 7 m depth. The densest SAV was observed by Batista et al (2012) at depths between 2 and 4 m in Taquaruçu reservoir (Paranapanema River, between Paraná and São Paulo State), showing SAV growing even at the depth range of 6-8 m. The status of SAV in Nova Avanhandava Reservoir (Tietê River, São Paulo State) was analyzed by Rotta et al (2016) who reported their occurrence at depths up to 9 m. The detection of bottom signal is difficult at such deeper waters even when using in situ sensing due to the attenuation and scattering of radiation in the water column. Rotta et al (2016) concluded that it is necessary to recalibrate and tune existing radiative transfer models with lots of field data in order to achieve the desired accuracy in mapping SAV biomass and height using satellite data.…”

“…Several other studies have concluded that high resolution airborne or satellite images may not be able to extract information about SAV in relatively deep reservoirs using frequently adopted simple methods such as image classification or empirical band ratios because of the target's low signal to noise ratio (Rotta et al, 2016(Rotta et al, , 2013Boschi, 2011;Malthus, 2017). Semi-analytical models have been proposed as an alternative to remove the water column influence and to retrieve bottom reflectance in water bodies to study submerged targets.…”

Estimating the Optical Properties of Inorganic Matter-Dominated Oligo-to-Mesotrophic Inland Waters

“…Infusion of nutrients (nitrogen (N) and phosphorus (P)) from the land via runoff often leads to eutrophication increasing the primary production of phytoplankton and macrophytes [3]. In oligo-to-mesotrophic reservoirs, the submersed species of macrophytes, which are usually rooted, occupy the edges and often the slow-moving zones of rivers [4]. They are dependent on the sediment supply and light availability for their optimal growth [5].…”