International Journal of Environmental Research and Public Health Article Analysis of Biogenic Secondary Pollution Materials from Sludge in Surface Waters Laima Cesonienˇ e˙ * , Edita Mažuolyte-Miškin˙ e,˙ Daiva Šileikiene,˙ Kristina Lingyte˙ and Edmundas Bartkeviˇcius Institute of Environment and Ecology, Faculty of Forest Science and Ecology, Vytautas Magnus University, Studentu˛str. 11, LT–53361 Akademija, Kaunas, Lithuania; [email protected] (E.M.-M.); [email protected] (D.Š.); [email protected] (K.L.); [email protected] (E.B.) * Correspondence: [email protected]; Tel.:+370-37752-224 Received: 18 October 2019; Accepted: 20 November 2019; Published: 25 November 2019 Abstract: Many countries of the world, including Lithuania, are making an effort to reduce surface water pollution. State monitoring data show that almost 80% of the lakes in Lithuania have an increased amount of sludge. One of the reasons for this increase in sludge is an excessive amount of biogenic material in the water. It is known that even after the source of pollution is removed, the condition of the lake water does not improve; rather, the condition of the lake water worsens due to the secondary pollution of sludge in the water. A study was conducted to determine the impact of secondary sludge pollution on water. For this study, 5 sludge samples were taken from different lakes in Lithuania. Fresh water was poured on the sludge samples, the concentrations of Nt, NO2-N, NO3-N, NH4-N, PO4-P, Pt, the pH and the changes in the electric conductivity (C) were measured in the water within 28 h. Research has shown that the thickness of the sludge layer influences the total amounts of nitrogen, phosphorus, and organic matter present in the sludge. As the thickness of the sludge layer increases in a lake, the total concentrations of nitrogen, total phosphorus and organic matter increase. Studies have also shown that the concentrations of all biogenic substances in water increase, with the exception of total phosphorus. This finding shows that organic phosphorus is "locked" in sludge, and no secondary pollution occurs from this source. Moreover, the electrical conductivity values of the water influence the release of biogenic substances from sludge in the water. Keywords: lakes; sampling; nitrogen; phosphorus 1. Introduction Water quality depends mostly on the characteristics and quantities of pollutants entering a body of water. In Lithuania, as in many European countries, the main water polluters are industry, agriculture, and households [1]. The factors determining the quality of surface water can be divided into direct and indirect factors. Direct factors (rocks, soils, biota, and human activity) remove or supply soluble chemical compounds in water. Indirect factors (climate, terrain, water regime, and vegetation, hydrological, and hydrodynamic conditions) produce an environment in which materials can interact with water [2]. The increased nutrients concentration enhanced the eutrophication, and, as a consequence, production of organic matter increases due to increased primary production. This has affected many water bodies, especially since the middle of the 19th century with the development of agricultural intensity and wastewater treatment plants [3]. Despite much research over the last five decades, eutrophication remains a major problem worldwide [4]. Lake ecosystems are particularly susceptible to anthropogenic effects, as they can become a reservoir of water pollutants and a main cause of the deterioration of the ecological status in inland and coastal waters [5–7]. In recent years, eutrophication in lakes has been one of the major ecological problems in the world. Most freshwater Int. J. Environ. Res. Public Health 2019, 16, 4691; doi:10.3390/ijerph16234691 www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2019, 16, x 2 of 17 Int. J. Environ. Res. Public Health 2019, 16, 4691 2 of 17 eutrophication in lakes has been one of the major ecological problems in the world. Most freshwater lakeslakes and and wetlands wetlands are are facing facing water water quality quality degradation degradation and and ecological ecological imbalances imbalances duedue toto growing growing anthropogenicanthropogenic activity, activity, especially especially in in developing developing countries countries [ 8[8].]. NitrogenNitrogen and and phosphorusphosphorus compounds compounds areare considered considered to to be be the the key key factors factors in in the the development development of of eutrophication eutrophication in in lakes lakes [ 9[9,10].,10]. TheThe transformationtransformation of nitrogen compounds compounds into into sl sludgeudge and and subsequent subsequent migration, migration, as aswell well as the as thereactions reactions between between sludge sludge and and lake lake water, water, are are important important processes processes in in the the biochemical cyclecycle ofof lakelake ecosystemsecosystems [ 10[10].]. TheThe nitrogennitrogen andand phosphorusphosphorus areare compoundscompounds thatthat promotepromote thethe primaryprimary productionproduction inin thethe lakeslakes thatthat cancan result result in in the the algal algal blogoms. blogoms. PhosphorusPhosphorus isis usuallyusually thethe limitinglimiting nutrientnutrient inin freshwater,freshwater, and and control control of of the the phosphorus phosphorus input input can can improve improve the the water water quality quality [ 11[11,12].,12]. ItIt hashas beenbeen foundfound that that the the “internal” “internal” pollution pollution ofof phosphorusphosphorus poses poses a a more more serious serious risk risk in in shallow shallow lakes lakes than than in in deepdeep lakeslakes [13[13].]. TheThe finestfinest particlesparticles areare usuallyusually foundfound inin thethe deepestdeepest areasareas ofof lakelake bottoms,bottoms, wherewhere relativelyrelatively intensive intensive sedimentation sedimentation occurs occurs due due to to the the production production of of phytoplankton. phytoplankton. SedimentSediment organicorganic mattermatter intensifiesintensifies biogeochemicalbiogeochemical nutrientnutrient overlaysoverlays onon thethe sludgesludge surface,surface, suchsuch asas mineralization,mineralization, denitrification,denitrification, oror phosphorusphosphorus relaxationrelaxation [14[14].]. AccordingAccording toto ŠaulysŠaulys [15[15],],phosphorus phosphorus entersenterssurface surface waterswaters byby being being flushedflushed fromfrom thethe soil,soil, rinsedrinsed outout ofof rocks,rocks,and and releasedreleased asas aaproduct product ofof vitalvital activityactivity andand thethe decompositiondecomposition ofof aquaticaquatic organisms.organisms. BottomBottom sedimentssediments areare anan importantimportant elementelement ofof lakelake ecosystemsecosystems because because they they are are involved involved in in internal internal nutrient nutrient cycle cycle processes, processes, and and the the main main role role of of bottombottom sedimentssediments is is to to accumulate accumulate nutrients nutrients [ 16[16].]. TheThe depositiondeposition of of phosphorusphosphorus from from sludge sludge to to water water and and its its transfertransfer to to the the trophogenic trophogenic zone zone may may be be more more intense intense than than its its sorption sorption and and deposition deposition [17 ].[17]. The The aim aim of theof the studies studies was was to determine to determine the the impact impact of secondary of secondary sludge sludge pollution pollution on water.on water. 2.2. MaterialsMaterials andand MethodsMethods LakeLake sludgesludge studiesstudies werewere carriedcarried out,out, consideringconsidering thethe depthdepth ofof sludge,sludge, organicorganic mattermatter content,content, nitrogennitrogen and and phosphorus phosphorus concentrations. concentrations. FiveFive lakes lakes were were selected selected for for detailed detailed research. research. The The reasonreason for forthe the choicechoice isis thethe highhigh concentrationconcentration ofof N N andand PP inin thethe sludge.sludge. AA total of 7–10 sludge samplessamples were taken from 5 didifferentfferent LithuanianLithuanian lakes:lakes: Kiementas,Kiementas, Sp Spera,˙ėra, Biržulis, Biržulis, Gauštvinis, Gauštvinis, and and Antakmeniai. Antakmeniai.Figure Figure1 1shows shows the the layout layout of of the the lakes. lakes. FigureFigure 1. 1.The The layoutlayout ofof thethe investigatedinvestigated lakeslakesin inthe theterritory territoryof of Lithuania. Lithuania. LakeLake Biržulis Biržulis is is locatedlocated inin westernwestern LithuaniaLithuania inin thethe TelšiaiTelšiai district,district, approximatelyapproximately 5 5 km km northeastnortheast ofof VarniaiVarniai (Figure (Figure1 )1) in in Varniai Varniai Regional Regional Park. Park. The The length length of of the the lake lake in in the the north-south north-south direction direction is is 3.63.6 km, km, and and the the width width is is 1.3 1.3 km. km. The The bottom bottom of Lakeof Lake Biržulis Biržulis is covered is covered with with sapropelic sapropelic clay, clay, sludge sludge and Int. J. Environ. Res. Public Health 2019, 16, 4691 3 of 17 Int. J. Environ. Res. Public Health 2019, 16, x 3 of 17 andclay clay sapropel sapropel in the in westernthe western and northernand northern bays bays and sandand sand along along the east the coast. east coast. In the In west, the west, the Varna the Varnariver flows river fromflows Lake from L ukštas,Lake¯ Lū andkštas, the and Nakaˇciariver