Sapro­pel. Char­ac­ter­is­tics, dis­tri­b­u­tion, appli­ca­tion

Sapro­pel is organ­ic silt deposits from con­ti­nen­tal water bod­ies (main­ly lakes) con­tain­ing more than 15% organ­ic mat­ter. In Ukraine, sapro­pel is a valu­able nat­ur­al resource with a wide range of appli­ca­tions in agri­cul­ture, med­i­cine, cos­me­tol­ogy, and indus­try.

Sapro­pel is includ­ed in the list of min­er­als of nation­al impor­tance approved by Res­o­lu­tion of the Cab­i­net of Min­is­ters of Ukraine No. 827 of Decem­ber 12, 1994, as an agro­chem­i­cal raw mate­r­i­al.

Characteristics and genesis

The organ­ic com­po­nent of sapro­pel includes bitu­men (3–11%), humic acids, and oth­er bio­log­i­cal­ly active sub­stances (up to 40%). The min­er­al part is rep­re­sent­ed by clay, sand, and fine-grained par­ti­cles. Among the min­er­als, allo­genic (quartz, feldspars, micas), syn­genet­ic auto­genic (opal, cal­cite, limonite, siderite) and dia­ge­net­ic (mar­c­a­site, pyrite, sul­fur) are dis­tin­guished. The den­si­ty of sapro­pel is about 1.05 g/cm³, and the water con­tent is 1.5–30 g per 1 g of dry mat­ter. The age of sapro­pel in mod­ern reser­voirs does not exceed 12 thou­sand years, but in a fos­sil state it can be trans­formed into sapro­pel coal or com­bustible shale.

Sapro­pel forms at the bot­tom of water bod­ies over a long peri­od of time and looks like a jel­ly-like mass, the con­sis­ten­cy of which varies from creamy in the upper lay­ers to denser in the low­er lay­ers. The col­or of sapro­pel varies from pink to brown­ish-olive and almost black. It con­sists main­ly of the remains of plank­ton­ic organ­isms, high­er aquat­ic plants and their decom­po­si­tion prod­ucts, as well as sol­u­ble sub­stances and min­er­al par­ti­cles that form a com­plex organo-min­er­al com­plex.

Accord­ing to the exist­ing clas­si­fi­ca­tion, sapro­pels are divid­ed into three main types: bio­genic, clas­to­genic, and mixed. These types, in turn, are divid­ed into six class­es: organ­ic, siliceous, organo-sil­i­cate, sil­i­cate, car­bon­ate, and fer­rug­i­nous. The name of the sapro­pel type reflects the com­po­si­tion of the organ­ic and min­er­al parts, their ratio, and ori­gin. In total, there are 14 types of sapro­pel. For each of them, quan­ti­ta­tive indi­ca­tors are estab­lished, such as ash con­tent, cal­ci­um and iron oxide con­tent, organ­ic mat­ter com­po­si­tion, and the typo­log­i­cal char­ac­ter­is­tics of the deposits in which cer­tain types of sapro­pel are formed are deter­mined.

Sapro­pel deposits are geo­log­i­cal for­ma­tions of lacus­trine ori­gin, con­sist­ing of lay­ers of one or more types of sapro­pel with a thick­ness of more than one meter. The exploita­tion of such deposits is eco­nom­i­cal­ly prof­itable.
Depend­ing on the con­di­tions of occur­rence, there are two types of deposits:

• Open – locat­ed in mod­ern reser­voirs, where sapro­pel accu­mu­la­tion process­es con­tin­ue to this day.
• Buried – lie under lay­ers of peat or min­er­al deposits.

Distribution of sapropel in Ukraine

In Ukraine, 308 sapro­pel deposits have been explored with total reserves of about 86 mil­lion tons. The largest deposits are con­cen­trat­ed in the Volyn region – lakes Svi­ti­az, Kulemetne, Luki, Tursk, Gorikhov, and oth­ers. Sig­nif­i­cant reserves are also found in Polis­sya, Rivne, and Cherni­hiv regions. These deposits are char­ac­ter­ized by a high con­tent of organ­ic mat­ter and great indus­tri­al poten­tial.

In the Volyn region, search and eval­u­a­tion work and detailed explo­ration were car­ried out on 191 lakes with a total area of 68.024 km². Accord­ing to data from the Kyiv Geo­log­i­cal Explo­ration Expe­di­tion, indus­tri­al reserves of sapro­pel in cat­e­gories A+C₂ amount to 69,987.2 thou­sand tons, of which 63,621.9 thou­sand tons are bal­ance reserves. Explo­ration and eval­u­a­tion work has been car­ried out on 115 lakes, as a result of which reserves in cat­e­go­ry C₂ are esti­mat­ed at 27,876.8 thou­sand tons, of which 23,580.8 thou­sand tons are bal­ance reserves. Detailed explo­ration was car­ried out on 76 lakes, where reserves in cat­e­go­ry A amount to 42,110.4 thou­sand tons, and bal­ance reserves amount to 40,041.1 thou­sand tons. In gen­er­al, the degree of explo­ration of lake sapro­pel deposits in the Volyn region reach­es 81%, with detailed explo­ration cov­er­ing about 32% of these deposits.

The largest explored sapro­pel deposits are locat­ed in the north­ern regions of the region, in par­tic­u­lar in the lakes of the Ratne, Turiysk, and Starovyzhivsk dis­tricts (40.8% of all deposits). Sig­nif­i­cant reserves have also been record­ed in the Kov­el (11.0%), Manevy­chi (10.0%), and Shatsk (9.4%) dis­tricts. In the cen­tral and south­ern dis­tricts of the region, such as Gorokhiv, Ivany­chi, and Lut­sk, the num­ber of lakes is sig­nif­i­cant­ly small­er, so sapro­pel reserves here are insignif­i­cant.

The lakes of the Volyn region con­tain the largest amount of mixed types of sapro­pel, in par­tic­u­lar organo-cal­care­ous (15,344.0 thou­sand tons), cal­care­ous (12,040.4 thou­sand tons), organ­ic-fer­rous (7,811.7 thou­sand tons), and cal­care­ous-fer­rous (231.0 thou­sand tons). The total bal­ance reserves of such sapro­pels amount to 43.7 mil­lion tons, which is 68.7% of all bal­ance reserves in the region. Reserves of clas­to­genic sapro­pels, which include organ­ic-sandy (3,766.9 thou­sand tons) and organ­ic-clay (5,097.9 thou­sand tons), are esti­mat­ed at 10.3 mil­lion tons, or 16.2%. The least com­mon type of sapro­pel in lakes is bio­genic sapro­pel, with a total of 9.6 mil­lion tons (15.1%) explored. This cat­e­go­ry includes mixed-algal sapro­pels (1,741.1 thou­sand tons), peaty sapro­pels (756.2 thou­sand tons), zoogenic-algal sapro­pels (5,148.0 thou­sand tons), and diatoma­ceous sapro­pels (1,030.8 thou­sand tons).

The ter­ri­to­ry of the Rivne region is char­ac­ter­ized by insuf­fi­cient study of lake sapro­pel deposits. Of the 81 exist­ing lakes, sapro­pel deposits have been esti­mat­ed in only 37 reser­voirs with a total area of 12.41 km², of which only 19 lakes have been cov­ered by detailed explo­ration. The total reserves of sapro­pel in cat­e­gories A+C2 amount to 13,900.0 thou­sand tons, which is 14.3% of the total reserves in Ukraine. The bal­ance sheet reserves amount to 8,381.3 thou­sand tons, which is 60.3% of the explored reserves. Explo­ration and eval­u­a­tion work has been car­ried out on 18 lakes, reveal­ing 7,012.8 thou­sand tons of sapro­pel in cat­e­go­ry C₂, of which 2,151.9 thou­sand tons (30.7%) belong to the bal­ance reserves. Detailed explo­ration showed that cat­e­go­ry A reserves amount to 6,887.2 thou­sand tons, of which 6,229.2 thou­sand tons (90.4%) belong to the bal­ance sheet. The esti­mat­ed resources of sapro­pel in 13 lakes amount to 1,231.0 thou­sand tons.

The explored sapro­pel reserves are uneven­ly dis­trib­uted across the region. The largest num­ber of deposits is locat­ed in the Zarich­nyan­skyi dis­trict, where 7,672.2 thou­sand tons of sapro­pel (55.2% of the region’s total reserves) have been iden­ti­fied in cat­e­go­ry A+C₂. In the Volodymyret­skyi, Dubrovyt­skyi, and Kostopil­sky dis­tricts, reserves exceed 1 mil­lion tons. Clas­to­genic types of sapro­pel, rep­re­sent­ed by organo-min­er­al (1,732.4 thou­sand tons), organo-clay (1,940.7 thou­sand tons), and diatoma­ceous-clay (61.5 thou­sand tons), account for 46.3% of the region’s total reserves. Such sapro­pels are usu­al­ly locat­ed in pro­found zones and cov­ered by oth­er sed­i­ments.

The largest sapro­pel deposits, with reserves exceed­ing 300 thou­sand tons, are locat­ed in the lakes Velyke Druhe (308.0 thou­sand tons), Luko (513.0 thou­sand tons), Ostrovatske (577.0 thou­sand tons), Verkhne (792.4 thou­sand tons), Nobel (4,308,000 tons), Maryanivske (1,218,200 tons), and oth­ers. The chem­i­cal com­po­si­tion of sapro­pel deter­mines its suit­abil­i­ty for var­i­ous uses, includ­ing agri­cul­ture, vet­eri­nary med­i­cine, cos­me­tol­ogy, and geol­o­gy.

There are 188 lakes in the Sumy region there are 188 lakes where 55 sapro­pel deposits have been dis­cov­ered with total geo­log­i­cal reserves of 6,699 thou­sand tons, of which 6,486 thou­sand tons are on the bal­ance sheet and 213 thou­sand tons are off the bal­ance sheet. Sapro­pel is not cur­rent­ly being extract­ed from these deposits. Sapro­pel reserves in cat­e­gories A+B+C₁ account for 2.36% of Ukraine’s total reserves. In 40 sur­veyed lakes, bot­tom sed­i­ments are main­ly rep­re­sent­ed by high-ash silt with lay­ers of high-ash sapro­pel with total reserves of 4,453 thou­sand tons.

In the north of the Kyiv region (Ivankiv and Vysh­gorod dis­tricts), there are two sapro­pel deposits (Val­o­vo, Svy­ate) with total reserves of 1.29 mil­lion tons, but they have not been mined recent­ly either. In the Cherni­hiv region, there are two promis­ing sapro­pel deposits with reserves of 60,000 tons, but they are not yet being devel­oped.

There are 36 lakes in the Kharkiv region, where 22 sapro­pel deposits have been dis­cov­ered with total geo­log­i­cal reserves of 6,456 thou­sand tons. In the reser­voirs of the Kher­son, Khmel­nyt­sky, and Ode­sa regions, sapro­pel is main­ly rep­re­sent­ed in the form of min­er­al silt with lay­ers of high-ash sapro­pel and peat. These deposits have sig­nif­i­cant poten­tial, but their devel­op­ment remains at an ini­tial stage or is not being car­ried out at all.

Application of sapropel

Sapro­pel is a valu­able organ­ic fer­til­iz­er that has a pos­i­tive effect on soil struc­ture, increas­es the con­tent of organ­ic sub­stances, pro­motes its sup­pres­sive­ness, and improves plant devel­op­ment. How­ev­er, its use in agri­cul­ture in Ukraine remains lim­it­ed. Accord­ing to the State Sta­tis­tics Ser­vice of Ukraine, in 2020, only 16.9 thou­sand tons of sapro­pel were applied to agri­cul­tur­al crops, which is 0.16% of the total vol­ume of organ­ic fer­til­iz­ers applied. This trend has been observed in recent years: in 2018, 18.0 thou­sand tons of sapro­pel were applied, and in 2019, only 3.3 thou­sand tons.

To ensure a bal­anced humus con­tent in the light soils of Polis­sya, it is nec­es­sary to apply 16–18 tons of organ­ic fer­til­iz­ers per 1 hectare of crop rota­tion area. Giv­en the decline in peat extrac­tion and the reduc­tion in cat­tle num­bers, sapro­pel could become an impor­tant source of organ­ic fer­til­iz­ers. In the west­ern region of Ukraine, sapro­pel reserves are suf­fi­cient for indus­tri­al extrac­tion. In addi­tion, sapro­pel can be used as a sub­strate in green­house veg­etable grow­ing, which is in line with the prin­ci­ples of envi­ron­men­tal safe­ty.

Today, sapro­pel is used as an organ­ic fer­til­iz­er in six regions of Ukraine, with extrac­tion of this resource tak­ing place only in the Volyn and Kyiv regions. In the Rivne, Sumy, Kharkiv, and Cherni­hiv regions, where there are sig­nif­i­cant deposits of sapro­pel, its resources are not used, despite the need for organ­ic fer­til­iz­ers and soil recla­ma­tion.

The largest amount of sapro­pel is applied in the Volyn region — 9.76 thou­sand tons, which is 58% of the total amount of sapro­pel applied. It is used even­ly for grow­ing cere­als, legumes, and indus­tri­al crops. In the Kyiv region, sapro­pel is used in small quan­ti­ties (0.004 thou­sand tons) for grow­ing fod­der crops. This indi­cates the sig­nif­i­cant poten­tial of sapro­pel, which remains under­es­ti­mat­ed in many regions of the coun­try.

In addi­tion, sapro­pel is wide­ly used in agri­cul­ture as a valu­able min­er­al and vit­a­min sup­ple­ment for ani­mals and birds. Their high effec­tive­ness as a feed sup­ple­ment is due to their sig­nif­i­cant con­tent of ben­e­fi­cial sub­stances, in par­tic­u­lar carotene and vit­a­min B12. These com­po­nents con­tribute to improv­ing metab­o­lism, strength­en­ing the immune sys­tem, and increas­ing ani­mal pro­duc­tiv­i­ty, mak­ing sapro­pel an indis­pens­able ele­ment in mod­ern ani­mal hus­bandry.

Com­pre­hen­sive lim­no­log­i­cal, geo­graph­i­cal, and bal­ne­o­log­i­cal stud­ies con­duct­ed by L. Ilyin and M. Pasich­nyk have proven the poten­tial of using lake sapro­pel from the Volyn region in recre­ation­al and resort activ­i­ties. Of par­tic­u­lar inter­est is the sapro­pel of Lake Velyke Pishchanske, whose reserves amount to 410,000 tons. Its prop­er­ties meet the reg­u­la­to­ry require­ments estab­lished for ther­a­peu­tic mud, which opens up wide oppor­tu­ni­ties for its use in bal­ne­ol­o­gy and health care.

Sapropel extraction

Despite sig­nif­i­cant reserves of sapro­pel in Ukraine, its extrac­tion is still under­de­vel­oped due to lim­it­ed invest­ment and out­dat­ed tech­nol­o­gy. For indus­tri­al devel­op­ment of sapro­pel deposits, the most prof­itable are reser­voirs with a sur­face area of up to 0.5 km², a depth of up to 4 m, and an aver­age sapro­pel thick­ness of more than 1.5 m. Such con­di­tions ensure effi­cient extrac­tion and min­i­mize devel­op­ment costs.

Since the main sapro­pel reserves lie under the water sur­face, the opti­mal method of extrac­tion is hydro­mech­anized. This method involves extract­ing sapro­pel using hydraulic pumps and then trans­port­ing the raw mate­r­i­al through main pipelines to a stor­age site or direct­ly to the con­sumer. This approach min­i­mizes the impact on the envi­ron­ment and reduces the cost of trans­port­ing the mate­r­i­al.

The use of hydro­mech­anized extrac­tion is advis­able for large reser­voirs with uni­form sapro­pel deposits. It allows for the extrac­tion of raw mate­ri­als in sig­nif­i­cant vol­umes for fur­ther use in agri­cul­ture, indus­try, cos­me­tol­ogy, and med­i­cine. The intro­duc­tion of mod­ern extrac­tion tech­nolo­gies and the estab­lish­ment of indus­tri­al devel­op­ment of sapro­pel deposits can sig­nif­i­cant­ly increase the effi­cien­cy of its use and con­tribute to the devel­op­ment of regions with rich deposits of this valu­able raw mate­r­i­al.

Despite its val­ue as a raw mate­r­i­al, sapro­pel also has a neg­a­tive impact on the eco­log­i­cal state of lakes. In many lake deposits in the Ukrain­ian Polis­sya, the fill­ing of basins with sapro­pel deposits reach­es 90%. Its accu­mu­la­tion in water bod­ies caus­es eutroph­i­ca­tion process­es, as a result of which lakes lose their abil­i­ty to self-clean, grad­u­al­ly become swampy, and their ecosys­tems are sub­ject to nat­ur­al degra­da­tion. The only effec­tive method to pre­vent this is to exca­vate sapro­pel. Remov­ing excess bot­tom sed­i­ments reduces their bio­genic impact on the water body, con­tribut­ing to the restora­tion of eco­log­i­cal bal­ance.

Indus­tri­al devel­op­ment of lake sapro­pel deposits also plays an impor­tant role in pre­serv­ing the ecosys­tem of water bod­ies. Sapro­pel extrac­tion con­tributes to the restora­tion of the water-drainage regime, increas­es the self-purifi­ca­tion lev­el of water bod­ies, and restores their func­tion­al­i­ty. At the same time, the raw mate­ri­als obtained can be used in var­i­ous sec­tors of the econ­o­my, such as agri­cul­ture, med­i­cine, con­struc­tion, and eco­log­i­cal land recla­ma­tion.

Thus, sapro­pel is a unique nat­ur­al resource with enor­mous poten­tial for agri­cul­ture, med­i­cine, and indus­try, and its ratio­nal use can become an impor­tant ele­ment in the devel­op­ment of Ukraine’s econ­o­my.