Abstract:
A submersible system is provided for isolating a volume of water located above an underwater substrate and for analyzing the volume of water. The system includes a tent having a shape enclosing an area of underwater substrate and a volume of water immediately above the substrate. A support frame formed by frame members each including plural detachable sections for maintaining the shape of the tent. A securing assembly, comprising a peripheral flap held down by weights in the form of sandbags or a heavy chain serves to secure the tent to the substrate. A circulation system, located at least partially within the tent, provides circulation of the volume of water within the tent so as to maintain a circulating flow pattern within the tent. A flow through analytical system is provided for removing a portion of water from the enclosed volume of water and for analyzing at least one property of the portion of water.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to submersible systems for monitoring and experimentation in aqueous ecosystems. More specifically, the present invention relates to a portable submersible in situ system for monitoring of, and experimentation with respect to coral reef ecosystems, coastal ecosystems and fisheries. 
     2. Related Art 
     The dangers to aqueous ecosystems from pollution and other processes are apparent, as is the need to act to preserve these ecosystems. Interest in gathering information on the processes and restoration of aqueous ecosystems, as well as interest in gathering information by experimentation on the effects of environmental perturbation on aquatic habitats, has greatly increased. This information is critical for assessing the health of aquatic ecosystems, for assessing environmental restoration progress, and for predicting the response of these ecosystems to climate change and declining water quality from natural and man-made influences. 
     In situ experiments measuring metabolic and geochemical processes associated with underwater organisms have been performed using very small (&lt;0.5 m diameter, &lt;4 liter volume) incubation chambers constructed of rigid Plexiglas or acrylic glass. These chambers effectively isolate a small volume of water about individual or small groups of underwater organisms enabling short-term (typically several minutes to a few hours) incubation experiments. These small chambers provide valuable information on processes associated with individual underwater species. However, accurate measurements of community level responses cannot be achieved using these small chambers. Additionally, these small chambers are not versatile and cannot be adjusted for size or volume to accommodate variations in substrate topography. These rigid chambers are limited in size due to difficulties in transporting and deploying larger chambers and in conforming and sealing the chambers to the often uneven substrate. 
     Community scale measurements of metabolic and geochemical processes have generally been performed using a technique called the “upstream/downstream” approach. This technique measures spatial geochemical changes in the water column along transects (generally greater than 100 m) across the substrate at the upstream and downstream ends of each transect. Currents/water circulation at the study site must be well characterized using current meters or other water mass tracking techniques. This method assumes conservation of water mass along transects, and is, therefore, limited to areas where unidirectional currents can be identified. Difficulties in accurately tracking the movement of a water mass result in the potential for a large margin of error. Many coastal ecosystems, such as coral reefs, have a complicated topography resulting in complex water circulation patterns. Thus, use of this technique is severely limited in its application. 
     Twenty-four hour monitoring along transects is logistically difficult due to problems in navigating along transects during dark hours. Most importantly, the upstream/downstream technique is limited by the resolution of geochemical measurements. Water must reside over the substrate long enough for its chemistry to be affected by processes of interest. Faster water flow rates result in shorter residence times and require a higher resolution for geochemical measurements to detect smaller chemical changes. Slower flow rates increase residence time of water over the substrates but most underwater organisms alter their metabolism when flow rate decreases, producing an abnormal response. 
     Structures resembling tunnels have been used to divert water flow in a modified upstream/downstream method. However, it has been found to be difficult to divert water flow over the long distances (100&#39;s of meters) typically required for accurate geochemical measurements with this method. 
     Therefore, there is a need in the art for a system that is portable, yet capable of accurately monitoring underwater habitats of various topography and currents therein at the individual organism, or community level. 
     SUMMARY OF THE INVENTION 
     According to the present invention, a portable system is provided for isolating, in situ, a large volume of water overlying a substrate in various aqueous environments. The system is designed to isolate the volume of water from the ambient aquatic environment, while maintaining contact between the captured volume of-water and the substrate components beneath it, including sediments and living organisms. The system provides for situ monitoring of physical and chemical characteristics of the water volume, monitoring of the components of the water, and associated monitoring of underwater organisms and substrates. Additionally, the system can be used for in situ manipulation of the physical and chemical parameters within the isolated volume of water for experimental investigations on the effects of environmental disturbances of the water, disturbances of components of the water, and disturbances of.the substrate. 
     In accordance with the invention, a submersible system is provided for isolating a volume of water located above an underwater substrate and for analyzing the volume of water, the system comprising: a tent having a shape enclosing an area of underwater substrate and a volume of water immediately above the substrate; support means for maintaining the shape of the tent; securing means for securing the tent to the substrate; a circulation system, located at least partially within the tent, for circulating the volume of water within the tent so as to maintain a circulating flow pattern within the tent; and a flow through analytical system for removing a portion of water from the enclosed volume of water, and for analyzing at least one property of the portion of water. 
     Preferably, analytical system includes means for returning the portion of water to the volume of water within the tent. 
     Advantageously, the submersible system further comprises means for removing trapped air from the tent. 
     Preferably, the tent further comprises a tent covering of a clear plastic material and at least one clear plastic tent door located at one end of the tent. Advantageously, the tent includes a further tent door located at the opposite end of the tent and the tent doors are attached by respective zippers to the tent covering. In a preferred implementation, the tent covering and the tent doors are comprised of a clear polyvinyl material. Preferably, the tent further comprises a bottom covering directly positionable on the substrate so as to separate the substrate from the volume of water. 
     The tent covering preferably includes a bottom peripheral flap extending outwardly therefrom so as to be positionable flat on the substrate and the securing means preferably comprises weight means positionable to provide weighing down of the flap so as to secure the flap in place. In one preferred implementation, the weight means comprises a plurality of sand bags, while in another, the weight means comprises a chain. In advantageous implementation, the flap comprises a reinforced flap extending outwardly from the bottom of the tent around the entire perimeter of the tent. In this implementation, the securing means advantageously comprises a plurality of sandbags located on top of the reinforced flap or a chain secured to the reinforced flap. 
     In a preferred embodiment, the support means comprises a tent frame comprising: a frame base for defining the substrate area enclosed by the tent; a plurality of frame ribs; a plurality of fittings on the frame base for attaching the frame ribs to the frame base; a frame spine; and a plurality of fittings on the frame spine for attaching the frame ribs to the frame spine. Advantageously, the frame base and frame spine each comprise a plurality of sections for enabling assembly and disassembly thereof. Preferably, the tent frame further comprises a plurality of metallic rods located within the frame base for assisting in maintaining the position of the frame upon the substrate. In this implementation, the frame base, the frame spine and the metallic rods each preferably comprise a plurality of sections for enabling assembly and disassembly thereof. Advantageously, the frame base, the frame ribs and the frame spine are comprised of polyvinyl chloride. Preferably, the frame base further comprises a plurality of pivoting stake supports. In a preferred implementation, the frame spine fittings comprise 90 degree fittings and the frame base fittings comprise T-fittings. 
     Other features and advantages of the invention will be set forth in, or will be apparent from, the detailed description of the preferred embodiments which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a submersible system constructed in accordance with a preferred embodiment of the invention, after assembly; and 
     FIG. 2 is a perspective view of selected parts of the system of FIG. 1, before assembly. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Turning first to FIG. 1, the system of the invention includes a tent  10  for enclosing the volume of water. The tent  10  includes a tent covering  12  which is described below and which, in this embodiment, is supported by a polyvinyl chloride (pvc) tent frame  14 . In a specific, non-limiting example, the dimensions of the tent frame  14  are 16 (l)×8 (w)×4 (h) feet, and the polyvinyl components are ¾ inch (diameter). As shown in FIG. 2, the tent frame  14  disassembles into eight foot sections for easy transport and reassembly. 
     Assembly of the frame  14  begins with assembly of a frame base  26 . Six eight-foot sections, indicated at  15   a,    15   b,    15   c,    15   d,    15   e  and  15   f  and collectively denoted  15 , are assembled to construct the frame base  26 , which, in the exemplary embodiment under consideration, has dimensions of 16×8 ft. The frame base  26  can be constructed above water and subsequently lowered into place on the substrate, or assembled below water, e.g., by scuba divers. The frame base  26  has twelve pivoting stake supports, two of which, denoted  37   a  and  37   b,  are shown in FIG.  1  and which are collectively denoted  37 . The stake supports  37  are adapted to hold three foot stainless steel stakes, two of which, denoted  38   a  and  38   b,  are shown in FIG.  1  and which are collectively denoted  38 . The stakes  38  are driven into the substrate as an alternate method for maintaining position of the tent frame  14  on an irregular bottom. 
     As shown in FIG. 2, the tent frame  14  also includes two sets of two eight-foot sections of stainless steel rod  36   a,    36   b  and  36   c,    36   d  which are respectively connected together by male and female connecting ends. The connected rods are placed inside the pvc pipe sections  15  lengthwise to add weight to the frame  14 , to maintain the position of the frame  14  on the bottom, and to prevent bowing of the frame base  26 . 
     As shown in FIG. 1, the upper portion of tent frame  14  includes a frame spine  32  which, as shown in FIG. 2, comprises alternating straight pvc sections  33 , and 90° pvc fittings  34 , adapted to be joined together. 
     To complete the tent frame  14 , fourteen frame ribs, two of which, denoted  28   a  and  28   b,  are shown in FIG.  1  and which are collectively denoted  28 , are inserted into respective spaced T-fittings  30  of the frame base  26  (best seen in FIG.  2 ). As indicated for a single rib in FIG. 2, the ribs  28  are each bowed and inserted at the other end thereof into a respective 90° pvc fitting  34  on the frame spine  32 . The frame ribs  28  thus each extend between a fitting  34  and a respective T-fitting  30  and, taken two at a time, an arch or bowed support structure. 
     After the frame  14  is assembled, the tent covering  12 , which is preferably made of clear vinyl, is fitted over the assembled frame  14 . A portion of the tent covering  12  is shown at the left side of FIG.  1 . In non-limiting example, the tent covering  12  is 21 feet in length and 16 feet wide, and of sufficient size to cover the frame ribs  28 . The center line of the tent covering  12  has a plurality of spaced grommet tabs  16 , one of which is shown in FIG. 1, spaced every three feet along spine  32  for attaching the tent covering  12  to the spine  32 . A pair of clear vinyl tent doors, one of which, denoted  18  is shown in FIG. 1, are attached to the tent covering  12  at opposite ends thereof in a final assembly step of the tent covering  12 , using a pair of eighteen foot zippers, one of which, denoted  20 , is shown in FIG.  1 . The tent covering  12  and tent doors  18  enclose and isolate a volume of water therein. The approximate volume of the tent  10  after being assembled and having the dimensions described herein is 7,809 liters. 
     A clear vinyl floor  22  can be inserted between the substrate and the tent frame base  26  so as to provide a barrier between the enclosed volume of the water and the substrate. The addition of the floor  22  completely isolates the volume of water within the tent  10  from the substrate. 
     An arrangement is provided for securing the tent  10  to the substrate, so that the tent  10  remains firmly in place even when the substrate is uneven or of pitched slope. In this regard, in the preferred embodiment shown in FIG. 1, a peripheral reinforced seal flap  24  extends from the edge of the tent covering  12  and includes flap grommets (not shown) spaced apart approximately every foot in a row about the seal flap  24 . A second row of grommets (not shown), is located near (e.g., about one inch from) the edge of the tent covering  12 . These grommets can be used in conjunction with the first row of grommets to secure a chain (a small portion of which, denoted  42 , is shown in FIG. 1) to the seal flap  24  and weigh the edges of the tent covering  12  down, while contouring the shape of the tent  10  to the bottom. 
     The tent  10  can also be secured in place on, and shaped or contoured to, the substrate by laying sandbags  40  around the perimeter thereof on the seal flap  24 . The sandbags  40  may be provided in addition to, or as substitute for, the chain  42 . In a specific non-limiting example, the sandbags  40  weigh 40-45 pounds and are constructed of five foot sections of drain sleeve filled with coarse grain sand, tied at one end, and cinched at the other end using zip ties (not shown). The sandbags  40  are laid on the seal flap  24  around the perimeter of the frame  14 . The sandbags  40  are overlapped end-to-end so as to contour the shape of the flap  24  to substrate and, similarly to the chain  42 , weigh the tent  10  down and hold the tent  10  in place along the bottom, thereby preventing leakage of water into or out of the tent  10 . 
     A circulation system located within the tent  10  maintains water flow within the interior of the tent  10 . As shown in the left hand portion of FIG. 1, this system includes a submersible 65 gpm (gallon per minute) circulation pump  44  which is mounted within the tent  10  on the frame spine  32 . A 16 foot (L)×3 inch (diameter) circulation hose  46  is attached to the circulation pump  44  at one end thereof. As illustrated, the circulation hose  46  extends along the top central portion of the tent  10  and, in this regard, circulation hose  46  is attached to the frame spine  32  at (e.g., six) spaced points along its length. The pump hose  46  extends along the frame spine  32  from the circulation pump  44  to the opposite end of the tent  10 , and the opposite end of the circulation hose  46 , i.e., the end not attached to the circulation pump  44 , is fitted to a 3 inch (diameter)×3 feet (L) pvc flow diversion tube  48 . The flow diversion tube  48  is very roughly in the shape of the letter “C” and includes a downwardly depending portion  48   a  and an inwardly directed portion  48   b  which faces towards pump  44  and serves reversing the direction of flow. Specifically, the flow diversion tube  48  diverts water flow in a downward direction from the circulation hose  46  located at the top of the tent  10  and the flow is diverted once more by portion  48   b  of the flow diversion tube  48 , so as to exit the flow diversion tube  48  while moving in a direction toward the circulation pump  44  located at the opposite end of the tent  10  and at a level lower than the water flowing from the circulation pump  44 . This diversion of water flow creates a circular flow path or loop which maintains a current inside of the tent  10  and thus prevents the water therein from becoming stagnated. Advantageously, the flexible nature of the tent allows oscillatory water motion, generated naturally by waves, to be translated through the tent walls to the enclosed water mass inside. A combination of oscillatory water motion and circulating water inside of the tent provides the most natural water flow regime for enclosed organisms. It will be appreciated that stagnation of the water, if permitted, would alter the metabolic response of most aquatic and marine organisms. 
     A hose  56 , which can comprise standard ¾ inch garden hose, is attached at one end of the flow diversion tube  48 . The hose  56  is used as an outflow hose to carry a portion of the water from within the tent  10  to the surface for analysis. Flow to the hose  56  is controlled and directed by a ball valve  50  disposed within the flow diversion tube  48 . The water is pumped by a second remotely located pump  62  from the outflow hose  56  to a remote analysis unit  58 . An inflow hose  60  is also connected to pump  62  and is used to return water to the tent  10  after analysis. The analysis unit  58  is used for analyzing various properties of the water according to application and/or need. In this regard, the analysis unit  58  is capable of analyzing water properties such as pH, dissolved oxygen, and salinity, and of removing water samples from, and of injecting chemicals into, the volume of water as necessary. As is evident from the foregoing, water is pumped back into the tent  10  in a closed loop, with the second pump  62  returning the water back to the tent  10  through the inflow hose  60 . 
     An air removal pipe  52  is attached to the top center of the tent  10  to expel air trapped during assembly of the system. In a specific non-limiting example, the air removal pipe  52  consists of a one foot section of ¾ inch pvc pipe with an associated ball valve  54 , a hose fitting (not shown) attached to the top at the pipe  52 , and first and second threaded plate fittings and associated first and second gaskets (not shown) at the bottom of the pipe  52 . More specifically, while other sealed connections can be provided in accordance with this embodiment, the first plate fitting is threaded onto the pipe  52  from the outside of the tent  10  with the first gasket facing downwardly. The pipe  52  is inserted into a hole in the top center of the tent  10  with the pipe  52  facing outwardly. At this juncture, the second gasket and fitting plate are threaded from inside the tent  10 . The gasket plates are tightened against the inside and outside of the tent  10 , respectively, to prevent leaks. The inflow hose  60  is attached to the pipe  52 . 
     The circulation system described above creates a horizontal flow across the tent  10  while the return flow from the inflow hose  60  of the water return system creates a slightly downward flow in the tent  10 . The cross flows provide better mixing within the tent  10 . 
     The tent  10  can be used to isolate large volumes of water over underwater communities to enable community-scale experimentation. Unlike the small incubation chambers referred to herein before, the tent  10  is versatile and can be adjusted in size to define different volumes and to accommodate a variety of substrate topographies. 
     The isolation of a mass of water provided by the system for monitoring and experimentation eliminates the need to track or follow a water mass over the substrate, as is required in upstream/downstream investigations of the prior art, and also eliminates the uncertainties of assuming conservation of water mass along transits. This results in more reliable analysis of community level processes. Further, water circulation can easily be altered in the volume defined by  10  for experimentation or standardized for experiment control. In addition, the system can be used to provide continuous, 24-hour monitoring of water mass and substrate ecosystem processes. Further, the system provides a mechanism for in situ alteration of environmental parameters such as salinity, turbidity, pH, and carbon dioxide content, thereby enabling investigations of the effects of environmental disturbances on underwater ecosystems. 
     In alternative embodiments of the invention to that described above include those providing variations in structural shape and size of the tent, and in the materials used in construction of the frame and tent, as well as modifications of frame style, the methods and mechanisms for weighting and sealing the tent to the substrate, and alternate methods and arrangements for providing water circulation within the tent structure. 
     It will be appreciated that the size of the tent  10 , including length, width and height, of the tent, the volume of water used, and the flow rate of the circulation system, can easily be adjusted using the approach described above. The length and width of the frame  14  can be easily increased or decreased by replacing the existing sections with longer or shorter sections or omitting or adding sections. The height can be decreased or increased by using either shorter or longer ribs  28 . The flow rate is readily increased or reduced by control of the ball valve  50  of the flow diversion tube  48 . Further, the tent structure may be designed such that the tent  10  requires no frame. For example, the shape of the tent may be maintained using flotation devices or by connection of the tent body to fixed or floating permanent or non-permanent structures on the substrate or surface, e.g., stakes, pilings, moorings, buoys, hooks, and the like. 
     The invention can be advantageously used in, but is not exclusively limited to use in, the fields of aqueous geochemistry, biogeochemistry, biology and hydrology. The system of the invention can be used to investigate substrate/water interactions, sediment/water interface processes, ground water flux studies, entrapment and investigation of biological organisms, and the effects of biological organisms on water column chemistry. 
     EXAMPLES 
     Example 1 
     The system of the invention as generally depicted in FIGS. 1 and 2 was tested in both deep (greater than 40 feet) and shallow (less than four feet) water in the Gulf of Mexico. The field tests included fluorescein dye injection studies to examine leak rates and mixing rates in the system, deployment of current meters for measuring current characteristics generated by the circulation system, measurement of attenuation of photosynthetically active radiation by the clear vinyl covering  12  used to construct the tent  10 , and 24-hour monitoring of the chemical changes in medium dense and heavily dense seagrass beds. 
     Fluorescein dye was injected into the tent  10  via a sample port in the flow through analysis unit  58  at night, and concentrations were monitored through the duration of the experiments using a model 10-AU Digital Fluorometer. 
     The data showed that approximately 24-30 minutes were required to mix water in the tent  10  and to reach peak dye concentrations. Results showed a slight decrease in fluorescein concentrations through dark hours consistent with rates of dye adsorption to sediments in organic materials, and concentration increases during light hours consistent with rates of photochemical decay of fluorescein. The rates of adsorption of dye to carbon sediment (2% of total concentration) and organic material (17% of total concentration) were used to generate a theoretical rate of concentration decay during the dark periods. This theoretical decay rate was used to correct raw fluorescence data to show decreases in night concentration associated with leakage of water into or out of the tent. Results showed no decrease in corrected dye concentrations. This indicates that there was no leakage of water during the incubation period. Fluorescein injection experiments indicated a water-mixing rate of approximately 24-30 minutes and no leakage at a circulation system flow rate of 65 gpm and a tent height of 4 feet. 
     Current speed and direction were measured in three dimensions. The results indicated that flow was not laminar and suggest that a turbulent flow may occur within the tent. The effects of the use of a clear vinyl sheeting or covering were examined by measuring attenuation of photosynthetically active radiation with water depth using a quantum sensor covered with a sleeve made from the same clear vinyl sheeting used to construct the tent covering for tent  10 . The same measurements were performed with the sensor uncovered. Preliminary results indicate that no difference in attenuation occurs between sleeved and unsleeved sensor data below a depth of three feet. 
     Example 2 
     Twenty-four hour geochemical monitoring experiments were performed by deploying the system of the invention at a medium dense seagrass bed in a basin, and on a heavily dense seagrass in a separate basin. In these experiments, the height of the tent  10  was reduced from four feet to two feet to accommodate the shallow water in the basins. The isolated water volume was left in contact with the underwater substrate comprised of seagrass beds. Geochemical parameters of the isolated water volume, e.g., pH, dissolved oxygen, fluorescence, and temperature were continuously monitored using a flow-through analysis system throughout a 24-hour incubation period. Water samples were taken from the flow-through system every four hours and mixed with mercuric chloride for alkalinity measurements via Gran Titration. The rates of net calcification (carbonate sediment production), photosynthesis, and respiration (collectively referred to as production) were calculated for each four hour interval. 
     Sample rates at intervals were used to calculate daily average production rates. Dissolved oxygen and pH data trends were consistent with photosynthetic and respiratory activity of seagrass beds during light and dark intervals. Average daily rates of photosynthesis for the two basins were 0.6 and 1.25 g carbon M −2  day −1 , respectively. 
     These are consistent with the range of values typically reported for seagrasses in the area of the basins. Calcification respiration calculations indicate net dissolution of 1.4 and 1.1 grams of calcium carbonate m −2  day −1 . The net evolution of respired carbon was 0.2 grams m −2  day −1  in the first basin, and net uptake of carbon was 0.1 g m −2  day −1  in the second basin. 
     Although the invention has been described above in relation to preferred embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected to these preferred embodiments without departing from the scope and spirit of the invention.