پایان نامه میزان نقش گیاهان آبزی در تولید ومصرف گازهای مختلف

پایان نامه میزان نقش گیاهان آبزی در تولید ومصرف گازهای مختلف

چكیده:

در مطالب جمع آوری شده میزان نقش گیاهان آبزی در تولید و مصرف گازهای مختلف و به بیان دیگر فتوسنتز در گیاهان مورد بررسی قرار گرفته است. اكثر اكسیژن محلول اضافه شده با گیاهان از میلیون ها جلبك سبز میكروسكوپی ناشی می گردد.

جلبك ها و گیاهان كاملاً غوطه ور در خلال روز از طریق فتوسنتز (فرآیند شیمیایی كه با آن گیاهان از خورشید انرژی بدست می آورند) اكسیژن به آب انتقال می دهد.

عموماً گیاهان غوطه ور در حدود 5 برابر اكسیژن بیشتر نسبت به مقداری كه مصرف می كنند به آب می دهند. اكسیژن محلول (Do) پارامتر كیفیت آب مهمی می باشد. اگر سطوح Do در بدنه آب به بیش از حد پایین افتد، ماهی ها و سایر ارگانیزم ها و گیاهان قادر به بقا نخواهند بود. گیاهان آبزی مختلف به روش های مختلف بر روی سطوح Do تأثیر گذارند.

Co₂ Equilibrium 8

Co₂ gas dissolved in water can take the from of bicar bonate or car bonate. These three forms are in chemical equilibrium which from is present in what amount dqpends on the pH.

 Bicarbonate ion  carbonate ion.  Dissolved Co₂

In the pH range favorablre to water plants , pH G. 4 7.2 /a percentage will be present as dissolved Co₂ and the rest as bicarbonate ions.

From pH 8.0 to pH 8.8 there will be almost no dissolved Co₂ , a large amount of bicarbonate and a small amount of carbonate.

Although they are named “water plants” most aquarium plants are really swamp plants that grow in their natural habitat with at least part of their levels above the water line. There fore, they have adapted to take up gaseous Co₂ from the atmosphere in the aquarium , placed under water, they are only able to use dissolved Co₂.

Several real water plants, meaning species, which are always under water in their natural habitat, are capable of also using the bicarbonate ion if Co₂ avail ability is limited. It is not however favorable to alou this to happens, firstly because many other plants in the aquarium will be unable to grow. Secondly with the use of bicarbonate ions the pH will rise to un acceptable levels for all plants.

Because of the Co₂ equilibrium discussed, the maximum amount of dissolved Co₂ present is dependent on the pH. The lower the pH the more Co₂ present. Since plants Co₂ in considerable amounts, they increase the pH at the same time. Thus the pH value and the Co₂ concentration are interrelated.

Carbonate harness (kH), is yet another factor that effects the concentration of Co₂ . Hard water , with a high kH can hold more Co₂ than soft water. While it is essentially true that hard water, with a low pH holds the largest amount of Co₂ in practice we can only use the values most suitable for plants, which are pH G.4-7 and 3-80 kH. The water plant enthusiast faces the task of maintaining both a stable pH and hardness in order to establish an optimum Co₂ concentration.

photosynthesis and oxygen production 8.

Photosyn the sis is a chemical process that takes place in many forms of bacteria and virtually all plants, including aquatic plants and algae. Using just three simple ingredients carbon dioxide, water , and sunlight- plants and bacteria are able to make their own food.

For tunately for all animals, including humans and fish, oxygen is a by-product of this miraculous process. As long as photosyn the sis is occurring, oxygen is continuously being released in to the air and in to the word’s lakes, oceans, rivers, and ponds.

Early forms of algae and bacteria uere the first organisms to photosynthe size , more than three BILLLON years ago. After a while , sign ficant amounts of oxygen had accumulated in the atmosphere. scieritists estimate that it takes about 2000 years of photosynthetic activity to “turn over” or replenish all the oxygen in earth’s biosphere.

Dissolved Inorganic carbon (DIC) is fresh water occurs as four different species in equilibrium with one another. The four speices of DIC are; carbon dioxide (Co₂) , Carbonic acid (H₂Co₃) , bicarbonate (Hco₃^-), and carbon. The total amount of DIC largely determines the determines the buffering capacity of fresh cater, and the vatio of these species with one another largely determines the pH.

Carbon dioxide dissolves, readily in water. An air equilibrium , the concentration of Co₂ in air and water is approcimately equal at about 0.5 mg/L.

Unfortunately, Co₂ diffuses about ten thousand times slower in water than in air. This problem is compounded by the relatively thick unstirred lager (or prandtl boundary) that surrounds aqutatic plant leares.

The unstirred layer in aquatic plants is a layer of still water through which gases and nutrients must diffuse to reach the plant leaf. If is about 0.5 mm thick, which is ten times thicker than in terrestrial plants. The result is that approximately 30 mg/L free Co₂ is required to saturate photosynthesis in submerged aquatic plants.

The low diffusivity of Co₂ in water, the relatively thick unstirred layer and the high. Co₂ concentration needed to saturate photosynthesis have prompted one scientist plants, the naturally occurring DIC levels impose a major limitation on photosynthesis …

The DIC limitations on aquatic macrophytes and its corollary, the need to conserve carbon, are becoming increasingly apparent as important ecological features of aquatic environments (George Bowes, Inorganic carbon Uptake by Aquatic photosynthetic organisms, 1985)

Aquatic plants have adapted to Co₂ limitation in several ways. They have thing often dissected leaves. This increases the surface to volume ratio and decreases the thickness of the unstirred layer. They have extensive air channels, called aerenchyma , that allow gases to move freely throughout the plants. This allows respired Co₂ to be trapped inside the plant and in some species even allows Co₂ from the sediment to diffuse into the levels finally, many species of aquatic plants are able to photosynthesize using bicarbonates as well as Co₂. This is important , since at pH values betueen 6.4 and 10.4 the majority of DIC in fresh water exists in the from of bicarbonate for the aquarist, the supply of Co₂ can be sugmented in two ways. Both methods work by first , the rate of water more ment in the aquarium can be increases. This will decrease the thickness of the baindary layer and ensure that Co₂ levels or at air equilibrium. This method is in expensive, easy to implement and will produce excellent growth of aquatic plants under most conditions.

Secondly , Co₂ can be injected in to the aquarium. This method can be expensive, and if done improperly, can be lethal of fish. This latter method is only essential , however , if there is a significant daily pH fluctuation in the aquarium , or if the species of plants being cultured are completely unable to use bicarbonate (Such as cabom ba sp.)