GB2504981A

GB2504981A - Sensing apparatus and method for measuring algal growth

Info

Publication number: GB2504981A
Application number: GB201214629A
Authority: GB
Inventors: Michael Bowes; Matthew O'hare
Original assignee: Natural Environmental Research Council
Current assignee: Natural Environmental Research Council
Priority date: 2012-08-16
Filing date: 2012-08-16
Publication date: 2014-02-19
Also published as: GB2507158A8; GB2507158B; GB2507158A; GB201314715D0; GB201214629D0

Abstract

A sensing apparatus for measuring and/or monitoring algal growth in a body of water comprises a light source; a light sensor arranged to sense light emitted from the light source; a data logger operably connected to the light sensor and adapted to record the intensity of the light sensed by the light sensor over a period of time; and a gap between the light source and the light sensor, within which algal growth can take place, when, in use, the sensing apparatus is at least partially submerged in the body of water; wherein, in use, algal growth within the gap is measured and/or monitored, as the algal growth affects the intensity of the light sensed by the light sensor and recorded by the data logger over the period of time.

Description

Measuring Algal Growth The present invention relates to the sensing and measurement of algae. More particularly, ii relates to the measurement and/or continuous monitoring of algae within a body of water over a period of time. The invention also relates to apparatus for sensing and measuring algal growth in a body of water.

Water is a precious natural resource. In order to help preserve, protcct and/or manage this resource effectively, it is important to be able to understand and monitor it, e.g. by obtaining reliable information on water quality and content. For instance, it may be desirable to sense and measure algal growth within a body of water such as a river, reservoir, lake or pond, since changes in the amount and/or types of algae present may indicate changes in water quality and/or iii the prevailing environmental conditions for plants and animals that live in the water.

For instance, it is known that blue-green algae is toxic and can cause serious illnesses in humans and animals. Thus, it generally may not be safe to swim in water containing bluc-green algae.

Currently, measuring and nionitoring algal growth can be a painstaking process involving the collection of individual algal samples by field operatives followed by time-consuming processing and analysis in the laboratory. Typically, the samples may be collected by scraping algae from rocks. It is estimated that in the south west of Scotland, the Scottish Environmental Protection Agency (SEPA) collects in excess of 400 algal samples per year. It typically can take a highly trained expert around half a day to process one sample in the laboratory, not including the time spent on sample collection or preparation.

It is known to measure and/or characterise algal growth in lakes using techniques which measure fluorescence or luminescence. A number of commercial products based on these techniques are available, e.g. the 6 series probes from YSI, Inc., the WetStar Fluorometer from WET Labs and the Algaelorch from bbe Moldaenke.

These products can be very sophisticated and expensive and may be susceptible to biofouling. Moreover, they may only be suited to taking single measurements and a field operative must be present to take each measurement. Thus, for instance, they may not be left in situ in a body of water to monitor algal growth continuously for a period of time.

A first aspect of the invention provides a sensing apparatus for measuring and/or monitoring algal growth in a body of water comprising: * a light source; * a light sensor arranged to sense light emitted from the light source; * a data logger operably connected to the light sensor and adapted to record the intensity of the light sensed by the light sensor over a period of time; and * a gap between the light source and the light sensor, within which algal growth can take place, when, in use, the sensing apparatus is at least partially submerged in the body of water; wherein, in use, algal growth within the gap is measured and/or monitored, as the algal growth affects the intensity of the light sensed by the light sensor and recorded by the data logger over the period of time.

The body of water may comprise any natural or man-made body or water, in which algae may grow. For instance, the body of water may comprise an ocean, a sea, an estuary, a river, a stream, a lake, a reservoir or a pond.

Typically, the sensing apparatus may comprise an at least partially transparent surface located between the light source and the light sensor, e.g. within the gap, on which, in use, algae can grow. The at least partially transparent surface may be substantially horizontal.

The provision of an at least partially transparent surface on which algae can grow may be advantageous, since it may allow for an assessment of algal growth on surfaces within the body of water. Such surfaces may include river, lake and sea beds and submerged equipment. Advantageously, it may be possible to measure and/or monitor biofouling of submerged equipment.

Accordingly, the sensing apparatus may be capable of measuring and/or monitoring algae growing within the water column (e.g. phytoplankton) and algal growth on surfaces within the body of water.

In contrast, known sensing apparatuses may typically be suitable for measuring algae growing within the water column (e.g. phytoplankton), but not for measuring algal growth on surfaces within the body of water as well.

In an embodiment, the sensing apparatus may comprise onboard power supply means operable to supply power to the light source and/or to the data logger. Alternatively or additionally, the sensing apparatus may be connectable to outboard power supply means, which may, for example, comprise a solar panel.

Typically, the light source may emit a known, quantified amount of light.

The period of time may be at least a week. Typically, the period of time may be weeks, months or even a year or more.

Accordingly, the sensing apparatus should be designed to be operable for such extended periods of time without human supervision or input. For instance, tile light source, the light sensor, the data logger and the or an onboard power supply means may be located in a protective housing, e.g. a substantially watertight unit or module, designed to prevent ingress of water and sediment or other matter within the water.

In an embodiment, the sensing apparatus may comprise a first substantially watertight unit or module containing the light source and a second substantially watertight unit or module containing the light sensor and the data logger.

The protective housing, e.g. the first and/or second substantially watertight unit or module, may provide the or an at least partially transparent located within the gap, on which, in use, algae can grow.

Optionally, the sensing apparatus may comprise one or more further sensors, e.g. a temperature sensor, a pH sensor, a flowmeter and/or a sensor for detecting sediment suspended in the body of water.

The sensing apparatus may comprise a support frame. Optionally, the protective housing, e.g. the first and/or second substantially watertight unit or module, may be permanently attached or attachable to and removable from the support frame.

Optionally, the sensing apparatus may be provided with securing means to hold the sensing apparatus, in use, at a given location within the body of water.

In an embodiment, the sensing apparatus may be providcd with means for varying the size of the gap. For instance, the sensing apparatus may comprise adjustment means operable to vary the gap.

The gap may be up to 15 cm across and/or at least 1 cm across. In an embodiment, the gap may be up to 10 cm across, e.g. up to 5 cm across. lO

A second aspcct of the invention provides a usc of at least one sensor according to the first aspect of the invention to measure and/or monitor algal growth in a body of water.

A third aspect of the invention provides a method of measuring and/or monitoring algal growth in a body of water comprising: * submerging at least partially within the body of water one or more sensors according to the first aspect of the invention; and * leaving the sensor(s) to measure and/or monitor algal growth in situ for a period of time.

A fourth aspect of the invention provides a method of measuring and/or monitoring algal growth in a body of water comprising: * shining light from a light source to a light sensor through a portion of the body of water; * recording the intensity of the light sensed by the light sensor over a period of time; and * using changes in the intensity of the light recorded over the period of time to measure and/or monitor algal growth within the portion of the body of water.

The method may further comprise providing an at least partially transparent surface within the portion of the body of water, on which algae can grow. The at least partially transparent surface may be substantially horizontal.

In order that the invention may be well understood, it will now be described by way of example only with reference to the accompanying drawings, in which: Figure 1 illustrates a laboratory set-up for testing the methodology of the invention; Figure 2 is a graph of some of the results obtained from tests carried out using the set-up shown in Figure 1; and Figure 3 shows a schematic cross-section through an embodiment of an algal sensor according to the invention.

Figure I shows a laboratory set-up comprising a test apparatus I. The test apparatus I comprises a base 2 and an upright support 3 extending upwardly from the base 2. The upright support 3 supports an arm 4, which is positioned above and a distance from the base 2. The base 2 houses a light source 5, while the arm 4 houses a light sensor 6, which is operably connected to a data logger (not shown). The light source 5 and the light sensor 6 are aligned such that light emitted from the light source 5 can be sensed by the light sensor 6. The base 2 and the arm 4 are provided with transparent windows (not shown) to allow light to travel from the light source 5 to the light sensor 6. An algal layer 7, i.e. a biofilm comprising algae, is shown on the base 2, between the light source 5 and the light sensor 6.

The laboratory set-up 1 shown in Figure 1 was used to investigate the effect of the algal layer 7 on the light sensed by the light sensor 6.

It will be appreciated that the base provided a surface, on which the biofilm grew.

Some of the results obtained from these experiments are shown in Figure 2. Figure 2 shows a graph of log dry mass of biofilm (grams) on the y-axis plotted against percentage reduction in light intensity on the x-axis. The percentage reduction in light intensity is measured relative to the light intensity detected when no algal layer is present for the same set-up, i.e. the same light source and the same distance from the light source to the light sensor.

The experimental results, as exemplified by the graph shown in Figure 2, indicate that there is a correlation between the mass of biofllm and the light intensity measured by the light sensor.

This correlation or relationship can be quantified and calibrated for different experimental set-ups, e.g. different light sources, different distances between the light source and light sensor and different types of algae.

Having shown that a quantifiable relationship exists, the applicants have realised that it may be used to help measure and/or monitor algal growth.

Figure 3 shows in cross-section an exemplary embodiment of an algal sensor 30 according to the invention. The algal sensor 30 comprises a base plate 31 with a support frame comprising an upright member 32 extending upwardly therefrom and a top member 33. The top member 33 extends laterally from the upright member 32, such that the underside of the top member 33 faces the upperside of the base plate 31.

A lower unit comprising a first protective housing 35 is mounted on the base plate 31 and next to the upright member 32. The first protective housing 35 comprises a first transparent window 38. A light source 36 and a power supply unit 37 operably connected to the light source 36 are housed within the first protective housing 35. In use, light from the light source 36 is directed such that it passes through the first transparent window 38.

An upper unit comprising a second protective housing 40 is mounted on the underside of the top member 33 and next to the upright member 32. The second protective housing 40 comprises a second transparent window 42. An integrated light sensor and data logger 41 is housed within the second protective housing 40.

There is a gap 39 between the bottom of the upper unit and the top of the lower unit.

The first transparent window 38 and the second transparent window 42 are aligned such that, in use, there is a direct light path across the gap 39 from the first transparent window 38 to the second transparent window 42, behind which is located the integrated light sensor and data logger 41.

In use, the first transparent window 38 conveniently provides a transparent surface located between the light source 36 and the integrated light sensor and data logger 41, on which, in use, algae can grow. Typically, a biofilin comprising algae may build up on the transparent surface.

As shown in Figure 3, the algal sensor 30 is provided with pegs 34a, 34b, which pass through apertures in a peripheral region of the base plate 31. Thus, the algal sensor 30 can be fixed to a surface, e.g. a river bed, using the pegs 34a, 34b.

The first protective housing 35 and the second protective housing 40 are designed to protect the components housed within them from ingress of matter, in particular water and any dirt or sediment entrained therein. For instance, the first protective housing and/or the second protective housing 40 may have an 1P68 rating.

A number of variations of the algal sensor 30 may be made without departing from the scope of the invention.

For example, the light source may be positioned above or below the light sensor.

The lower unit and/or the upper unit may be permanently fixed to the support frame or they may be removable. Advantageously, the lower unit and/or the upper unit may be releasably securable within the support frame. Thus, for example, the lower unit and/or the upper unit be removed at the end of a study and quickly replaced with a new unit or units for a subsequent study. Similarly, fixing or maintaining the algal sensor during a study may be facilitated. For instance, if a component were to fail, e.g. the light source stopped working or there was a problem with the power supply unit, then it would be a simple matter to remove the unit containing the failed component and fit a new, replacement unit in its place. Further, it may not be necessary to recover the support frame from its site of use after a study has been carried out.

The gap should be appropriately dimensioned such that algal growth can take place within the gap and is not hindered or constrained by the gap. A gap 39 of around 2.5 cm between the top of the lower unit and the bottom of the upper unit has been found to give acceptable results. [-lowever, the optimum gap size may vary depending on a number of factors, including, for instance, the light source used and the intended site of usc. The climatic conditions and the time of year may affect the growth of algae and may also need to be taken into account.

Typically, the gap may be up to 15 cm across and/or may be at least 1 cm across.

S

The algal sensor may be provided with means for varying the size of the gap 39. For instance, adjustment means may be provided, which may be operable to adjust the position of the top member on the upright member, thereby allowing the distance between the upper unit and the lower unit to be varied. Alternatively or additionally, inserts may be utilised in order to vary the gap between the upper unit and the lower unit. For instance, one or more inserts may be secured between the base plate 31 and the lower unit and/or between the top member 33 and the upper unit.

The light source may be constant, variable and/or controllable, e.g. from a remote location. The light source may comprise a white light source. Optionally, one or more filters may be employed, in order to select specific wavelengths. Alternatively or additionally, the light source may be designed or engineered to emit only certain specified wavelengths. Certain wavelengths may be better suited for detecting given types of algae, e.g. blue-green algae.

The light source may comprise one or more light emitting diodes (LEDs). The use of LEDs may be preferred since they emit well-defined wavelengths of light.

Furthermore, LEDs are typically relatively small and reliable, have long lifetimes and relatively low power requirements and do not emit much energy as hcat.

The power supply unit may comprise a battery. Typically, the power supply unit may be selected such that it will provide sufficient power for the duration of the period the algal sensor is in situ.

In some embodiments, power may be supplied to the algal sensor from one or more solar panels located above the water level and connected to the algal sensor. The solar panels may provide primary or back-up power to a single algal sensor or to a network of algal sensors, e.g. a network comprising a plurality of algal sensors within a given body of water. Solar power is intermittent. Accordingly, the algal sensor may be provided with storage means for storing energy supplied from the solar panels for use at night or on cloudy days.

The or each protective housing may be openable. Accordingly, at the end of a study, the light sensor and/or data logger and/or light source and/or power supply unit may be rcmoved from their respective protective housings. New components may be placed and secured within the protective housings for use in subsequent studies, e.g. to meet different requirements and/or to replace broken, faulty or worn out components.

It is not essential that the light sensor and data logger are integrated. Nevertheless, a suitable integrated light sensor and data logger is the 1-IOBO Pendant® Data Logger 64K from Onset Computer Corporation, whichalso includes a temperature sensor as well as a light sensor. Data can be taken from this integrated light sensor, temperature sensor and data logger for processing and analysis by plugging it into an Optic USB Base Station which can be connected to a computer.

Advantageously, the algal sensor may comprise one or more further sensors in addition to the light sensor. The one or more further sensors may be operably connected to the data logger and may include, for instance, a temperature sensor, a pH sensor, a water flow meter and/or a sensor for detecting sediment in the body of water.

The additional data collected by these further sensors may help to understand and/or explain the amount of algal growth that is measured.

The data logger may typically be provided with output means for sending recorded data for processing and analysis. The output means may be connectable to a computer, either directly or indirectly though use of a portable memory storage device.

Optionally, the algal sensor may be provided with data transmission and/or receiving means, which may be operable continuously or intermittently, e.g. at predetermined intervals, during a study. Accordingly, algal growth may be monitored, typically remotely monitored, on an ongoing basis, potentially even in real-time, during a continuous study ovcr an extendcd period of time. Furthermore, operation of the sensor may be controlled in response to changes in conditions. Also, the algal sensor may be checked and/or fixed and/or maintained, if the data being received indicate that the algal sensor has stopped working normally. A further advantage is that potentially dangerous levels of algal growth may be detected more quickly and, if necessary, appropriate safety measures may be implemented.

Various means for securing the algal sensor in place at a site of use may be employed.

For instance, the algal sensor may be provided with one or more downwardly facing spikes on its base, either instead of or in addition to separate fixing means such as pegs, nails or screws. Alternatively or additionally, the algal sensor may be held in place using weights, e.g. rocks, which may, for example, be placed on a peripheral portion, e.g. flange of the base plate.

On occasion, it may not be desirable or practical to fix thc algal sensor to the bottom of a particular body of water. Accordingly, the algal sensor may be attached or attachable to a submerged portion of a buoy, pontoon, pier, jetty or the like.

On occasion, it may not be desired that the algal sensor be fixed in one place.

Accordingly, the algal sensor may be fitted to, e.g. to an underside of, a boat or raft.

Alternatively, it may be fitted to a submerged porion of an untethered buoy.

Alternatively, the algal sensor may be fitted to a manned or unmanned submersible vehicle.

The algal sensor may be fitted with tracking means, e.g. OPS location means.

Accordingly, the location of the algal sensor may be tracked, e.g. if it were to be disturbed or unexpectedly removed froni a fixed intended site of use and/or if it is not fixed in one place and is free to move around a body of water.

Use of the algal sensor 30 to measure and monitor algal growth will now be described.

The light source 36 and the integrated light sensor and data logger 41 are turned on and the algal sensor is fixed to a river bed using the pegs 34a, 34b. The algal sensor is then left in situ on the river bed for a period of time, typically weeks, months or even years. During the period of time, algal growth within the gap 39 is monitored by changes in the intensity of light detected by the light sensor. At the end of the period of time, the algal sensor 30 is recovered from the river bed and the integrated light sensor and data logger 41 is removed from the upper protective housing 41. The data stored on the integrated light sensor and data logger 41 is then extracted and transferred to a computer for processing and analysis.

Advantageously, the algal sensor of the present invention is relatively simple and not too expensive. Moreover, it is reliable and can be left in situ within a body of water

II

for extended periods of time. Accordingly, algal growth can be monitored, e.g. continuously monitored, over longer time periods, without requiring a trained operative to be present.

Accordingly, the invention may allow for the more efficient collection of data on algal growth than is currently achievable. The invention may allow continuous monitoring of algal growth. The invention may also allow for the collection of more data from more locations, without significantly increasing the number of peoplc involved in the collection of the data.

Advantageously, by providing an at least partially transparent surface on which a biofilm comprising algae can build up while the algal sensor is in situ, the algal sensor may allow for reliable monitoring and/or measurement of algal growth on surfaces such as river, lake and sea beds or submerged equipment. This may be useful in assessing biofouling of submerged equipment.

A plurality of algal sensors according to the present invention could be used to carry out a wider survcy of a body of water such as a river, reservoir, lake or pond. Each algal sensor could be placed at a different site within the body of water, where it would sense algal growth. By looking at the data collected froni each location, it niay be possible to build up a picture or map of algal growth across the body of water and how this varies with time.

Continuous monitoring whether by a single algal sensor or a wider survey using a plurality of algal sensors may provide useful information for predicting the conditions within a body of water and nianaging use of the water.

It is envisaged that the apparatus and methods of the invention may also bc used to detect and/or measure and/or monitor various plant or animal types, species and varieties other than algae, e.g. other fonns of biofilni growth, present in a body of water or other fluid.

Further, it is envisaged that the invention may have utility in measuring and/or monitoring the quality and/or purity of any body of liquid, as long as the liquid is at least sufficiently transparent at least some of the time to allow light to travel from the light source to the light sensor.

Claims

Claims 1. A sensing apparatus for measuring and/or monitoring algal growth in a body of water comprising: * a light source; a light sensor arranged to sense light emitted from the light source; * a data logger operably connected to the light sensor and adapted to record the intensity of the light sensed by the light sensor over a period of time; and * a gap between the light source and the light sensor, within which algal growth can take place, when, in use, the sensor is at least partially submerged in the body of water; wherein, in use, algal growth within the gap is measured and/or monitored, as the algal growth affects the intensity of the light sensed by the light sensor and recorded by the data logger over the period of time.
2. A sensing apparatus according to claim 1 further comprising an at least partially transparent surface located between the light source and the light sensor, on which, in use, algae can grow.
3. A sensing apparatus according to claim I or claim 2 further comprising onboard power supply means operable to supply power to the light source and/or to the data logger.
4. A sensing apparatus according to claim 1 or claim 2 or claim 3 comprising a first substantially watertight unit or module containing the light source and a second watertight unit or module containing the light sensor and the data logger.
5. A sensing apparatus according to any one of the preceding claims comprising one or more further sensors selected from: a temperature sensor, a pH sensor, a flowmeter and a sensor for detecting sediment suspended in the body of water.
6. A sensing apparatus according to any one of the preceding claims, wherein the sensing apparatus is provided with securing means to hold the sensing apparatus, in use, at a given location within the body of water.
7. A sdnsing apparatus according to any onc of thc preceding claims, whcrcin thc sensing apparatus is provided with means for varying the size of the gap.
A sensing apparatus according to any one of the preceding claims, wherein the gap is up to 15 cm across and/or at least 1 cm across.
9. A scnsing apparatus according to any onc of thc prcccding claims comprising one or more filters operable to select specific wavelcngths of light emitted by the light source. I0
10. A scnsing apparatus according to any onc of the preceding claims, whcrcin thc light source comprises at least one light emitting diode.
11. Use of at least one sensor according to any one of claims 1 to 10 to measure and/or monitor algal growth in a body of water.
12. A method of measuring and/or monitoring algal growth in a body of water comprising: * submerging at least partially within the body of water one or more sensors according to any one of claims Ito 10; and * leaving the sensor(s) to measure and/or monitor algal growth in situ for a period of time.
13. Thc usc of claim 11 or the method of claim 12, whcrcin the body of water comprises an ocean, a sea, an estuary, a river, a stream, a lake, a reservoir or a pond.
14. A method of measuring and/or monitoring algal growth in a body of water comprising: shining light from a light source to a light sensor through a portion of the body of water; recording the intensity of the light sensed by the light sensor over a period of time; and using changes in the intensity of the light recorded over the period of time to measure and/or monitor algal growth within thc portion of the body of water.
15. A method according to claim 14 further comprising: providing an at least partially transparent surface within the portion of the body of water, oii which algae can grow.
16. The use of claim 11 or claim 13 or the method of any one of claims 12 to 15, wherein the period of time is at least a week.
17. A sensing apparatus substantially as described herein with reference to the accompanying drawings.1. A method of measuring and/or monitoring algal growth in a body of water substantially as described herein.