Heavy Metal Concentrations and Sediment Quality of a Cage Farm on 1 Lake Volta, Ghana

12 This study involved the determination of sediment quality and heavy metals in the water 13 column and bottom sediment of a selected cage fish farm in Lake Volta, to assess the potential 14 impact of metals and organic matter pollution on the lake due to cage fish farming. Sediment 15 analysis indicated that the texture of all sampling sites was sandy clay loam with sand 16 dominating with a range of 31.5 – 81.2%. The Organic matter (TOM) ranged from 4.42 – 17 8.89%, while organic carbon (TOC) was from 2.57 – 5.22%. Total nitrogen (TN) fluctuated 18 between 0.22 and 0.45%; total phosphate ranged between 0.22 and 5.30%. The TOC, TOM, 19 and TN content in the farm sediment were significantly lower than those of the reference sites 20 (ANOVA, p<0.05). Lead, copper, cadmium, and selenium were not detected in the water. The 21 results revealed that heavy metals concentrations in the water column and sediments were low 22 and within tolerable levels, indicating no influence of metals from fish feed was observed on 23 the lake water quality. However, the farm seemed to have moderate impact on sediment quality 24 from organic matter. Water and sediment quality monitoring should be embarked upon 25 periodically to ensure sustainable cage culture in the Lake Volta.


Introduction
while being stirred until a sharp green colour change was noticed at the endpoint. Reagent 152 blank (deionized water) was run using the above procedure without sediment to standardize 153 the ferrous solution after which the carbon content of the sediment was determined. The total 154 organic matter was calculated as % organic matter = 1.7 x % organic carbon (Allison, 1965).  The sediment samples were oven-dried and 0.3g of the dried sample was digested using HNO3 171 (8ml, 65%) and HF (2ml, 40%) mixture in a 'milestone' Ethos microwave digester (START 172 D) at 180° C for 45 min. The solution was diluted to the 50 ml mark and left overnight to 173 promote precipitation of suspended solids. Then, the digested sample (0.5 ml) was pipetted into 174 a 50 ml flask followed by its dilution to 25 ml. The phosphate determination was performed at 175 880 nm using T 60 UV-Visible spectrophotometer following molybdate complex formation

195
The sampled water (100 ml) was filtered with 0.45 µm pore size filter papers. 68 % HNO3 was 196 added to the samples until the pH was less than 2. The water samples were then analyzed for

Water Quality Parameters
The mean, standard deviation, minimum and maximum values of the water quality parameters 232 at the study area are presented in Tables 1. Surface water temperatures were found to be 233 uniform at all sampling sites and exhibited temporal variations. The pH values of the surface 234 water ranged from 6.4 to 8.7 and those of the reference site varied between 6.6 and 8.8. For the of the metal concentrations detected in the water column was as follows: Fe > Mn > Zn > Cu 265 = Pb = Se = Cd. No significant difference was observed between the farm and the reference 266 site as far as the metals' concentrations are a concern. Nevertheless, a correlation existed 267 between Zn and Mn (r =0.0.315, p < 0.01), Fe and Mn (r =0.509, p < 0.01) and Fe and Zn (r = 268 0.664, p < 0.01), in the farm.

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The particle size analysis showed that the texture of the sediment was sandy clay loam at all 327 the sampling sites (Figure 3). The sand content in the sediments analyzed had a range of 31.5 328 -81.2 %. The larger the diameter of sediment particles, the higher the ability of the 329 environment to recover from the impact caused by waste accumulation (Kemp et al., 2011).

330
With the sand pre-dominating the sediment, the monitoring sites will have the potential to 331 recover from any waste accumulation. Measurement of ORP is done to determine the organic 332 enrichment of the sediment. In undisturbed sediment, the ORP value is about 300 to 400 mV  The amount of TOC and TOM, TP and TN in sediment is useful in the determination of 341 sediment contamination. It is estimated that for a zone to be considered as uncontaminated, the 342 content of organic matter in the sediment must range from 0.5 to 5 %, whereas the sediments 343 with more than 15 % organic matter are typical in contaminated zones (Méndez, 2002). The reported TOC levels of 5.4-8.59 % in a rainbow trout cultured reservoir. They reported that no significant differences in metals concentrations between the farm and the reference site in 391 the water column (Mwamburi, 2009).

392
The heavy metal levels observed in the sediments in this study were all lower than the threshold 393 effects concentration (MacDonald et al., 2000). The variation in the content of the lake's 394 sediment was shown in the metal distribution. Selvaraj et al., (2004) reported that high sand

408
The knowledge of environmental impacts of cage culture is vital to the protection and 409 management of aquatic resources. The results obtained revealed that the tilapia cage culture 410 that was studied in Lake Volta did not significantly impact the quality of the lake with regards 411 to heavy metals pollution. The results showed that the concentration of heavy metals in the 412 water column and sediment were low and within tolerable levels suggesting no impacts from 413 feed additives. However, the farms seemed to have a moderate effect on sediment quality with 414 respect to organic matter which is difficult to attribute solely to impact from the cage since data 415 on pre-farm sediment quality was non-existent. The minimal impact of the cage aquaculture 416 could be attributed to possible dispersion of cage waste by the water currents, and reduction of 417 nutrients by dilution. The levels of the water quality parameters (turbidity, DO, pH and 418 conductivity) from the farm were not significantly different from those of the reference site 419 indicating that the water quality parameters were not affected by the cage farming activity. The 420 oxygen levels encountered during the monitoring period is suitable for tilapia production and 421 ecosystem use. With the expansion in cage operations in the lake, nutrient loads will continue 422 to increase and that will produce considerable pollution into the lake's environment. For sustainable development of cage culture in Lake Volta, it would be useful for stakeholders to Kingston, H., & Walter, P. (1995). Microwave assisted acid digestion of siliceous and Winsby, M., Sander, B., Archibald, D., Daykin, M., Nix, P., Taylor, F., & Munday, D. (1996).

584
The environmental effects of salmon net-cage culture in British Colombia. Report 585 prepared for the Ministry of Environment, Lands andParks, 1106-1175. captions Table 1: Mean±SD concentrations and ranges (in parenthesis) of surface, bottom and reference sites for some physico-chemical parameters in the fish farm Table 2: Sediment particle size distribution and soil texture of the Farm Table 3: Mean±SD and range of metal concentrations (mg/L) in the water column of the farm Table 4: Mean and range of metals, ORP, and pH in the sediment of the farm

Figure 1
Cage fish farming and heavy metals in Lake Volta

Figure 2
Cage fish farming and heavy metals in Lake Volta

Figure 3
Cage fish farming and heavy metals in Lake Volta