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Bilindigi tizere dogal siirecler sonucunda olusan ban yer sekilleri insanlann ilgisini ceken onemli dogal turistik kaynaklardir. Ozellikle morfodinamik siireclerle cok Iuzli olusumlar goriildiigi: karstik yorelerde, dogal anit niteligi tasiyan cok cesitli sekiller gelismistir. Karstik birikim sekillerinden biri olan travertenler de bu olusumlardan biridir. Ulkemizde Denizli Pamukkale Travertenlerine benzeyen, hatta minyatiirii saytlabilecek traverten sahalarindan biri de Van ili Baskale ilcesi Akcali koyiinde yer almaktadir. Soz konusu traverten sahasi yaklasik lOOx200 I1l boyutlannda, yuzlerce eskive yeni basamakli havuzlartyla olaganiistii bir giizellige sahiptir. Traverten-sahastnda 10'a yakut kaynak ve 7 m yiiksekten dokiilen bir de faglayan bulunmaktadtr. Bu calismada tanituni atnaclanan Akcali Travertenleri ulasuni zor, biiyiik merkezlerden uzak, henliz turizm acistndan degerlendirilmeyen karstik bir olusumdur. So; konusu dogal turistik kaynak, cevresindeki diger turistik cekiciliklerle (Van Gala, Siiphan Dag), Netnrut Dagi, CUo Dag: gibi) bir biaiin olarak degerlendirilmesi halinde yore ve idke ekonomisine yarar saglayacaktlr. It's known that some of the earth shapes which becomes as a result of some tiaturel processes and draw people's attention (Ire important nature! touristic sources. Especially, a variety of earth shapes like naturel monuments are formed at tnorpliodynamical process and l'el)' rapidly occured karstic places. The travertines which are karst accumulations are one ofthose formation. One of the mini travertines which is similar to Patnukkale is located at Akcal: village, in Baskale-Van. The area of travertines is about 100 x 200 tn It has extraordinary beauty and hundreds of old and new stepped pools. In this area there about 10 wells an done waterfall whose height is 7 tn. The Akcal: travertines, explanied/described in this study, far ([tvayfrom big city centres, difficult to visit by car, not used for touristic purposes, is a karstic formation. If Akcali travertines are considered with other nat/rei touristic sources like Van Lake, Siiphan, Nemrut and Cilo Mountains. It is fine that the Akcali travertines will contribute to the economies of local cities and country ofTurkey

The abundance of phytoplankton, thermohaline conditions and concentration of nutrients were determined in the highly stratified Zrmanja Estuary, eastern Adriatic coast, Croatia, in the period from June 1998 to October 2000.

Periphyton assemblages (algal biofilms) can be important factor for majority of production in shallow, unshaded, coastal aquatic habitats. The karstic river Zrmanja (69 km) discharges into the eastern–central Adriatic Sea, and forms shallow, highly stratified estuary. The distribution of attached diatoms on artificial substrates and those in plankton was analyzed in the upper reach of the estuary in July 2000. The sharp halocline was detected in the 1–1.5 m layer. The brackish layer above the halocline (14 PSU), and marine layer (30-34 PSU) bellow the halocline was detected. Thermic conditions (19 to 24 şC) were characterized by subsurface temperature maximum in the halocline. The extremely low concentrations of nutrients (orthophosphates 0.02-0.06 mmol L-1, nitrates 5.3-7.6 mmol L-1), and high oxygen saturation (80-90%) indicated oligothrophic character of the estuary. The euphotic layer extended to the bottom (4 m deep). The maximum abundance of penatae diatoms (9.6 x 107 cells cm–2) was registered after 16 days of colonization in the upper reach of the estuary. The similar abundance was found after 28 days of colonization. The attached penatae diatom Cocconeis scutellum reached the abundance of 105 cells cm-2 after 16 days, while 3.8 x 105 cells cm-2 after 28 days of colonization, in the brackish layer. The local anthropogenic input of nutrients resulted in the 11% and 15% greater abundance of total attached pennatae diatoms, and C. scutellum, respectively. In plankton, C. scutellum was mostly distributed in the 1-3 m layer (400-6400 cells L-1). The outflowing current above the halocline detached cells from the substrate and transported them down the estuary. The population successively sank and accumulated around the halocline, died in the layer of strong gradient of salinity and continued to sink to the bottom. Due to transport by currents, suspended C. scutellum cells were 30% more abundant at the 6 km downstream station. The population was not detectable in the middle reach of the estuary where salinity increased to 34.51 PSU.

The taxonomic composition and abundance of phytoplankton were analyzed in relation to thermohaline and hydrological conditions in the middle reach of the karstic river Zrmanja Estuary, eastern Adriatic coast, Croatia, in the period December 1981 to November 1982, and June 1998 to June 1999. General trophic interrelations were characterized by the spring-summer development of marine phytoplankton (mainly diatoms) and autumn- winter development of small herbivores (copepods, nauplii, copepodites). Two maxima of naked ciliates indirectly indicated the regeneration of alochtonous organic matter in winter, and autochtonous organic matter in late summer. In general, dominant phytoplankton species provided seasonal recurrent assemblages. Freshwater phytoplankton above the halocline is less abundant in the lower than in the upper reach of the estuary. Instead of freshwater phytoplankton, the brackish diatom Thalassiosira (a short-chained, small- celled species) was abundant above the halocline during the winter-spring period.

The status and data on the biology of hondrostoma phoxinus,an endem. species of the Croatian, Bosnia and Herzegovina border, are presented. This species has a peculiar biology, often occurring in small springs, stagnant and underground waters. Body form and small scales indicate specialisation to karstic environment. Ten years ago some authors identified C. phoxinus as the most abundant species in the natural Lake Busko blato in Bosnia ar Herzegovina, which belongs to the same Cetina watershed. In Croatia, the species occurs only in Sinjsko polje and is very rare despite the fact that the area of main occurrence is very close. In major investigations of the Croatian distribution area, within the Cetina river system, C. phoxinus was not registered. Introductions of alien species, especially the invasive ones from the Danube watershed, such as Lepomis gibbosus, Ictalurus nebulosus, Pseudorasbora parva, an Carassius auratus gibelio greatly jeopardise its survival. Recently, natural habitats of C. phoxinus described previously with only twelve species, have completely disappeared.